The official word from PTerry is that the “out-of-character” patrician is Vetinari, but written by a much less experienced author. All other patricians are his temporary replacement, or his predecessors who are mentioned as historical people, or seen in flashback.
Marchesa isn’t a problem of history, but geography.
Krull is a place that’s incredibly hard to get to and almost impossible to escape from. Unseen University has no authority there, and as such can’t impose the rule that women can’t be wizards.
Granny Weatherwax might insist that women can’t be wizards because of other reasons than tradition, but Esk managed, and it’s amazing what you can accomplish if you don’t know that it’s impossible.
As to Esk being referred to as “the first female wizard”, it’s like how Sir Roderick Purdeigh was the first man to set foot on Bhangbhangduc - anybody else was foreign, and therefore doesn’t count.
“Sometimes things just happen. What the hell.”