Or maybe other ideagroups dont go far enough.
The reason things like Humanist or Admin or Influence look good on paper and are good in practice is the "uniqueness" or their mechanics.
Admin isn't a good example here: it's a mess of an idea group that randomly has one overpowered idea, which is too broad to favour any specific playstyle (blobbing isn't really a playstyle, more the default behaviour of players). Influence on the other hand has a fairly consistent theme and several powerful ideas.
Take the Trade group. It is an absolute joke compared to having just a handfull of small CNs or owning enough provinces in 3 TCs.
You can replace the effect of the entire group with mechanics that exists elsewhere in the game.
If trade wanted to compete with just playing the game it would have to give some 20 merchants and 100% trade-eff or something.
Trade is a really weird one to place. It certainly has its problems, but I wouldn't say it's a complete write-off:
- The +merchants are actually very useful in the base game. It's just that a couple of DLCs have been far too generous with bonus merchants, so everyone has too many of them in single player. Tone those down or add some more preconditions, and Trade could have a clear purpose again. For instance, what if you didn't get +merchants by default from TCs, and instead that was the Trade finisher? Somehow the devs need to balance this idea group so it makes sense both with and without DLCs (like how the Economic finisher is different with/without Common Sense, but both versions are valuable).
- Leaving the merchants issue to one side, the point of the idea group is to make money, and if you compare to other idea groups that directly improve your economic efficiency (as opposed to letting your conquer more etc), it's not so bad once you take into account policies, and the general potential of trade to make money compared to other income sources. Trade+Quantity has some interesting synergies as a TC-heavy power, for instance. It's just that such purely economic modifiers are probably never going to be strong enough carry an idea group on their own, because if they were, they'd just end up being another factor in the oversupply of ducats in the game. The goods economy especially suffers from being a 'rich get richer' system, i.e. blobs are not just richer in absolute terms, they generally get more goods income *per development* than lesser powers do, so bonuses to goods-based income go disproportionately to countries that are already too rich to need it.
More broadly though I think you make a good point. Some ideas are real game-changers, while others just give you a slight edge; the same with policies, which in some ways is worse because you end up with a situation where many policies are simply never worth activating. I get the impression that the devs have tried to make things 'balanced', it's just that they consistently overrate some modifiers and underrate certain others, sometimes to a dramatic extent. (This is even before we get to ideas that have a qualitative effect, such as Deus Vult.) So for instance, you get ideas and policies that give super niche bonuses like rebel support efficiency, trade range or vassal force limit contribution, and it's never at a level that would change how anyone plays; then you look elsewhere, and they're casually handing out discipline, diprep or -global unrest as if it's an equally minor bonus.