Hmmm, I get that Hive worlds are more efficient for specialist output, but I'm not convinced that being able to expand your world and thus just keep generating *more* slots for specialist workers beyond the starting planet size doesn't have more value.
The only specialists who scale with planet size are Industrial District alloy workers, and a 10% specialist buff is (not really in aggregate but go with me) basically 2 pops per 10 districts. All other planet-based specialists are limited by building cap.
Adding that since hive worlds are made with energy- a nearly unlimited resource in the game- but world expansion is gated by influence, an extremely limited resource- and you can more easily increase all outputs in your empire by 10% than you can increase your planetary alloy capacities by 10%. And even that assumes that it's district size and not pops that's the limiting factor- most people have the issue of too few pops and too many planets.
In my experience hives have plenty of influence late-game, and habitats take a comparatively long time to pay off.
I mean, habitats are conceptually the mutliplication of space-based resources, and +2 growth slots. Nearly every resource in space gives you multiple times it's base amount if you build a habitat on it,
and you're generating more pops to exploit it via colony ship
and increasing empire growth overall. If you're not suffering from an alloy shortage, it's the best way to expand your resource and science base short of war, and if you're going to war you have better uses for influence than +1 district.
Plus, while my argument for expanding the world is based on maximising use of deposits for fun - it can also be used to produce just more specialist slots for alloys. With any bonuses from buildings on that world already baked in, without having to set up the additional infrastructure on a habitat.
If you find it fun that's all it needs to be, conversation over, but alloy specialist slots really aren't a limited thing. The influence (and energy) you expend on them could just as well be used to other, greater, purposes that have bigger economic impact in the short, medium, and long term.
I can't help but feel that bigger worlds that do both basic and specialist resources are just better/comparable if you focus on using habitats primarily on science deposits instead of resources.
Edit: Especially if you use catalytic processing.
Not really, no. Well, yes, habitats are best at science and strategic resource deposits, but planetary industry is the least efficient industry
because it mixes basic and specialist resource production.
In terms of basic (worker) resource production, nothing beats planets. Planetary 25% boost outmatches the Habitat equivalent designations, which is 10%.
But in terms of industry (alloys), Habitats are basically just as good as planets, since a planet isn't getting the resource buff if it's designated as industry, or not getting the industry buff if designated as resource world. Habitats
not already used for science/strategic resource deposits basically have no opportunity cost with focusing on industry and efficiency, because you aren't losing out potential basic resource production benefits. There is a question of strategic resource efficiency, but if you're building habitats and using their pops for alloy districts you have building slots to spare for refinery buildings- or even entire refinery habitats, to fuel more alloy worlds.
The only way for Hives to boost their alloy production efficiency is either via Ring Worlds (where they can get a 10 jobs per district and a 5% boost from designation; a trade of alloy-inputs for admin capacity-pops and pop-output) or a Hive World (where less admin-capacity savings, but higher pop output bonus AND the resource savings.)