They should have just left them as money grubbing assassins like they were in DF, instead of injecting them with "Sithis". But we have been over this before.
I agree. But then again, different branches could have different agendas and "cultures". Daggerfall and Morrowind (I think at least, I do not remember how the DB appeared to be in Morrowind and Tribunal) DB is by heritage ruled by greedy bastards, who make sure their chosen "disciples" (e.g. those who they favor and promote) are of the same mind. In Cyrodiil, a different group came to power, possibly over the years, or maybe right from the start, putting focus on religion and rituals. Both paths could just be different ways to maintain order and strict regulation over their followers.
And on a side-note, I think that the "Sithis" they worship, as well as their "Night Mother", are nothing but Meridia still imposing her influence on them. You don't get rid of Daedra Princes that easy, do you.