A 5% tech discount isn't that much overall; it's nice, but not a selling point. Admin points are more scarce than mil/diplo when you're blobbing, anyhow, so the 10% admin tech cost off admin will rate equal/better all by itself, never mind RCC. Prestige - once you get going, you're generally throwing it away by gaining 50 prestige while you already have 99. Get some triggered modifiers + religious + great power and you can be /gaining/ prestige while at 99 prestige. It's kind of absurd, really.
The war exhaustion reduction is great, especially if you can't get DoTF, but not enough to sell the group all be itself. Institution embracement is meh. There are only so many institutions to embrace, it won't save you that much over the course of the game, and mega-blobbing usually leaves you with tons of cash by the time you hit the last institution or two.
In other words, it's not really strong enough to justify taking it over all the other idea groups you probably want, and most of the things it does well are done as well/better somewhere else. If you're playing tall, Econ and exploration (to colonize) or trade (if you're playing land-locked) will be much better money wise. Econ will save you a ton more money on buildings/unit costs, while making you tons of money and saving you quite a few MPs on developing if you're outside of Europe or just developing instead of conquering. You'll want military ideas as well, since you wont have the built-in quantity of a ton of development; you'll need quantity ideas and/or the "big three" quality boosters - def/off/qual.
If you're blobbing, admin, humanist, influence, diplo are all pretty well locked in. Admin and Diplo ideas have Admin/Diplo cost discounts built in on top of being otherwise very strong groups (diplo allows you to reduce war exhaustion for reduced cost, for instance). Influence will also save you a ton of dip points if you don't take religious, as well as it being a must-have for making use of vassals, dealing with aggressive expansion, etc. Humanist for separatism if nothing else, taking religious /and/ humanist isn't actually a bad call. Military ideas generally play well here also, as more mil quality = less money spent on quantity, easier, faster wars, etc.
Innovative really isn't /bad/, it's just not good enough to compete with the best options. If you want variety in ideas, it's hardly going to cripple you, it's just not the strongest group out there.
