I agree with that. Promotion should be based on results more than unmeasurable numbers. I'd say to get in the guild at all you'd need decent skills they desire, but past the entry, promotion would be based on dedication and time serving. Then make the quests harder for people without the skills required by the organization. Have a quest in the Mages Guild where you have to cast the spell Banish Daedra, straight up. No getting around that one, you can either do it or not.
Though this system wouldn't work if there were spell scrolls. Remove the spell scrolls from the game.
I agree with the scrolls. Get rid of them. Anything that you could really need (restore strength, fatigue, health) can come in potion form. It would then open up the possibility of receiving magic tomes for spells that could not be learned by non-magic people, not just because the book for some reason requires some specific number destruction skill, but rather because you could not even hope to earn it without the skill.
Overall, I was pretty disappointed with the FG and MG quests in OB. They were really just "do it to say you did it" type questlines. You didn't really get anything out of them, save money, which seems really stupid. Sure, you gained access to a spell vendor with different spells, but what about the libraries in the arcane university? It should have been a real achievement to gain access to it, and it should have been because you were enabled to learn an abundance of new (not necessarily REALLY powerful) spells. And as you continued to gain rank, you should have become privvy to much higher level spells, capable of much greater effects than you could have as a lowly member. You could have done similar things with the fighter's guild, giving the player more powerful moves and maybe even...hold on now...COMBOS! Or the ability to disarm an opponent through sheer blade skill! There were so many possibilities, and they really fell short in my opinion.
Edit: some more speling.