It's not just that it's pretty implausible - I think the guilds lose any sense of depth when they become a pet organization.
True. Dark Brotherhood works because no matter what, you are always taking 'orders' from the Night Mother. Only way you can genuinely become the leader of a guild is if the quest line is actually long enough to justify you pushing your way to the top through being awesome and proving you have what it takes. Any thing else just looks forced, hence why the College questline is so atrocious...
Decided to start a 3rd char (My highest is only lvl21, though it did take me 26 hours to reach lvl21 as mage and only 9 to reach lvl16 as archer) just to see how melee combat was and how things were in the Companions. Fighting the Dragon was... painful. Its biting wasn't that strong but the burning took 3/4 of my health down easily.