I think they over did it in Oblivion. I remember after becoming the leader of 3 guilds, I started seeing where that was going on. It was a long process to become the leader of the guilds. But by joining all these guilds, the rules sort of overlap each other. For example the thieves guild and their no kill policy conflicted morally with the Dark Brotherhood and their kill everything in your way policy. I think when making Oblivion they didn't expect people to just join the mages guild, fighters guild, thieves guild, etc., etc. all at the same time. Why would your assassin join the Mage's guild? Or why would a barbarian join the Thieves guild? Each guild was made for different kind of characters, so when you completed the quest it felt more justifiable to be the leader.
I think in Skyrim they should make it to where there are pre-requirements to join a guild. IE: must be skilled with a bow or have high sneak to join thieves guild. To see if you meet the requirements they could send you on a quest that would be difficult without those skills. That will keep all the posers out.