As someone else pointed out, Spiritualist do not have a particularly high faction approval. Theirs is actually rather anemic. Other ethics have a higher base one and much easier time.
This misunderstand the argument. The value of Spiritualist in an ethics build is their 'good enough' approval to get the relevant bonuses of faction approval combined with a high ethics attraction modifiers, which are seperate from ethic weighting biases (that are also good). This is
speed of conversion argument, combined with what the bonuses of faction approval actually are.
Speed of conversion is a relevant consideration due to how non-slave living standards give unequal but considerable political weight to conquests. Egalitarians have an ok-faction approval of 80%, but egalitarian living standards put all pops on roughly the same weighting. This means if you conquer pops of anti-ethics, you will significantly
fall in faction-outputs because your Egalitarians have much less of a share of your empire %. In time they will convert (and speeding this up is the point of the Egalitiaran-specific edict), but in that time you take a much steeper penalty. Lid and I disagree on the speed argument based on our readings/experience with % modifiers; I find them stronger than basic weighting mechanics, but he has assumed they were weak weighting basis.
The benefits from faction bonuses is a separate item. There's three benefits of having pops in happy factions: a unity-per-pop benefit, a happiness-per-pop modifier that affects stability, and avoiding the penalty of
not being in an unhappy faction.
The unity-per-pop faction influence is basically a wash that goes to Spiritual favor due to Spiritualist's 10/20% unity for all sources, including but not limited to faction unity, in a meta where unity is, while not a critical requirement, a major wide-scaling one if you want major powerspikes of later traditions. On its own in terms of factions, Spiritualist 10% means an effectively 10% higher approval level than listed, because even if their approval is 'only' 50 for some notional 50% of .5 unity for .25 per pop, they're still getting 10% from that. This still peaks lower than Xenophile- everything does- but that's not the point.
The point is this faction unity argument is itself a red herring, because unlike in 3.2- when factions produced Influence which was an irreplacable resource- in 3.3 they produce unity, which is also now the main output of Ruler Pops, and unity is a valuable efficiency resource in the early game (for moving your pops to get colonies to size 10, which improves their growth efficiency and also gives more Rulers faster), and a resource you have to dedicate production to in order to get your late-game power spikes. The more resources you have to dedicate (pops and planets), the more unity beyond the factions you need. The more production you dedicate, the smaller a share of your faction unity is.
All of this unity- from wide ruler pops, from trade builds, from unity worlds- is getting boosted by Spiritualist.
The faction unity argument is akin to arguing planes are slow because a car can outrace them on the taxiway. This is true. This is also irrelevant. Spiritualists are not worse at the unity game than other empires on the basis of factions, because factions are not the basis of the unity game. The tradition value of Spiritualist isn't the first two or three traditions, but the next five or six, when faction unity was never going to be enough to reach it reasonably.
The second benefit of faction bonuses is the happiness modifier. Happy factions offer two buffs to pops: +5% when faction approval is 60-79%, and +10% happiness when 80+%. There is no scaling bonus to this- 100% faction approval is as happy as 80%. This is what I'm referring to when I talk happiness (as opposed to approval), though I do slip from time to time.
This is where 'good enough' matters, due to what the benefits of happiness actually are.
-Every point of happiness above 50 is +1% chance to adopt state ethics.
This is useless for a pop that is already a member of state ethics. Happy xenophiles don't become more likely to become xenophiles.
-Every point of happiness above 50 is -.02% crime, to a max of 0. This is nice, but far from major.
The biggest asset is popular approval, which is the planetary average of happiness modified by .6% stability per point of approval. A 5% difference in faction happiness- which is the difference between a 60-approval Spiritual and 100 approval xenophile- amounts to... a 3% stability boost. 3% stability is a 1.8% boost to all jobs.
(In a very generous assumption scenario where we just handwave the time it takes to get there.)
That's not
nothing, but it's tiny in the sea of modifiers. Planetary habitability differences- which you can mitigate by moving pops around with unity and energy- dwarfs that.
And this is where the 'spiritualists can't have robots' argument becomes a meme. Factions start at 50 approval. Having robots is a -5 modifier. Being a spritiualist empire with 10% of the population as spiritualist is +15 in modifiers. You're
already at the 60% plateau where the biggest difference is 2% pop output.
The third benefit of having cohesive, happy factions is avoiding the penalty of
unhappy factions, and this is where points 1 and 2 work in tandem- it's far more important economically to
avoid penalties than to
maximize faction happiness. This is because
unhappy factions have a -10% happiness modifier at 20-39 approval, and a
-40 modifier at 0-19, and the penalties for unhappiness are much steeper.
Every point of pop unhappiness is-
-1% ethics attraction
-.02 crime per point, up to +2 crime per pop at 0 happiness (starts at base 40)
And in terms of popular approval
-1 Stability, where every -5 stability is 3.1% economic decrease
Together these faction penalties mean that conquered pops are
slower to integrate if they're antithetical to a faction- say autoritarian-slave conquests brought into a xenophile-no-slave build- and while they will eventually convert, in this time non-stratified living standards give these pops plenty of political influence in your faction economy (decreasing unity gained) and in your planetary stability economy (mitigating faction happiness buffs). This, in turn, is disrupting your early snowball potential, where early-game faction unity matters most for early traditions, and maintaining decent stability is key for re-utilizing your conquests to fuel more conquests.
This is where Spiritualist flexibility and ethics attraction % modifiers comes in. As a faction, Spiritualist is policy-wise not at odds with anyone
but materialists. Unlike no-slaver xenophiles, it can more easily adjust it's policies to its captured pops (or even enslave them to mitigate their political power), appeasing factions to avoid the greater penalties which- in turn- reduces the time it takes for the pops to convert to spiritualist. This ties to other spiritualist ethics % modifiers in less time.
As for conquest and expansion. Spiritualist have no bonus to this. In fact unless they use robots they will actually fall behind. Because pops directly translate into economy, and economy translates into being able to expand and conquer. Which then results in more pops and more economy.
This misunderstands the war synergy of Spiritualist and economics of robots. Robots are an anti-early war pop bloom strategy, and pop blooms are inferior to military builds for pop accumulation.
Robots are a very expensive investment more akin to habitats than fleets when it comes to expanding your economy. They take 2 alloys, 5 energy, and a pop, and don't even
stop being net-losses until about the fourth pop built. This is because it takes the first robot pop to 'match' the pop invested as the assembler, the second to cover the energy upkeep, and the third to cover the alloy requirement. Only at the fourth pop do you
start to make back the investment with net productivity, but with pop assembly being about 5 years (or more) a pop, this is a nearly 20 year delay of accumulating costs, and nearly 480 alloys for those two decades.
Per planet, mind you. So for a modest 8 planet early empire, you're looking at over 3800 alloys not-used on fleets that could conquer an empire doing so in these first 20-30 years.
Spiritualists- in so much as they 'can't' or 'shouldn't' have robots- are free to use these alloys precisely to conquer the sort of empires that would and adding those pops to their own, a significant early-game war economy base that far outpaces what robot empires can accrue in the early game.
(Which, again, they can totally be themselves. They just bypass Synthetics/AI, which is not a requirement for success.)
Moreover, Spiritualist builds can absolutely build themselves to draw Psionic Ascension reliably in the early game once the tier 3 techs start opening, due to how the Psionic weights work. Psionic isn't just the fastest ascension to unlocks, but the best for early-game warmongering to get your snowball speeding up. Psionic Rulers gives influence (for claims) and ethics attraction (for incorporating unhappy faction conquests), governors give stability (best for war-boosting specialists like scientists and alloys), Psionic scientists innately get research buffs that put Intelligent psionics on par with Erudites, and Pyschic Admirals get direct damage
and evasion buffs, most useful for early-game corvette and destroyer swarms.
Psionic is absolutely an ascension for early-game snowballing to simply outmass peaceful pop-assemblers who go synth, Psionic itself ties handily to Spiritualist, and we return to Spiritualist (if no robot) not only having many more alloys to dedicate to early conquest fleets,
but also being completely compatible with other war-mongering ethic combos like Authoritarian or Militarist (or both).