I'm going to accuse you of what I see you doing. The first half of your post I quoted is speculation or assumptions. Which of those words you use depends on how much you agree with them. I did take the more combative term off the start because I disagreed with your speculation, for which I apologize.
To me it looked like you were passing your speculation as fact here:
It would, if you read each sentence in isolation.
In aggregate, it seems pretty clear that the thrust of my argument was and is speculative.
Not declarative.
I do not have the power to make Word of God declarations here.
I'm also going to disagree with your speculation on the colleges mapping at all to normal religous life in the empire.
With the possible exception of the Jade College, who apparently do recruit internally in this AU from families who have been mages for at least a generation or more, most of the other colleges draw their recruits from the mass of the Imperial population.
Plus, Warhammer Fantasy is apparently not the Star Wars Jedi. They don't seem to grab unformed young children, even from the orphanages.
Possibly because children that age require looking after.
Significant numbers of named wizards also seem to be recruited at ages old enough to already have opinions on religion before coming to the Colleges. Balthasar Gelt was old enough to pay his own way to Altdorf. Verspasian Kant had already spent several years learning at the libraries of Marienburg and then a year in an orphanage. Van Horstmann was already a fully fledged follower of Tzeentch.
And anecdotally, I will note that no one accuses the Colleges of being a godless institution.
Not conclusive, mind, but in an Empire where gods are empirically proven phenomena, religion is serious business, anti-magic suspicion is common and the wrong god can get you burned, it's yet another piece of data.
So no, I feel there is significant evidence to argue that religious life in the colleges is likely to bear a strong resemblance to the populations it recruits from. Not identical, but a recognizable relative.
EDIT
Even then only the Templars of Sigmar are actually Sigmarites. Many witchhunters belong to secular authorities or one of the other cults of the empire.
The official, state-sponsored Templars, who operate Empire wide with the Emperors explicit backing are members of the Cult of Sigmar.
A cross between the FBI and the Inquisition.
As far as I know, they are the only ones that the Colleges, which means us, are legally obliged to render assistance to on request.
The rest are everything from vigilantes to the equivalent of private eyes and county deputies or, if I'm being generous, state police.