I haven’t done all the DB quest but so far I don’t really like any of them, the vampire girl is annoying too.
Maybe you’re thinking of how the Thieves Guild was in Oblivion. The thieves guild in Skyrim are not honourable nor do they claim to be. Everything is for profit. Even their reason for not killing anyone is not out of honour, its more because it complicates things and is a pain in the ass to cover up.
Really? These "mercenaries" do things like clear giants from nearby towns, get rid of harmful animals from places, clear out bandit hideouts, and even save kidnapped civilians. Does that seem like a bunch of ruthless mercenaries? Not all of them want to be part of the "conversion".
Not everything they do is quite so honourable. They also take jobs like beating [censored] out of someone to “settle an argument”. So basically being a thug for hire.