That's not how filmmaking works. Just because it doesn't make sense to us doesn't mean Hadida might not have been a part of it, because executive meddling boils down to essentially "I don't like this, so change it, and don't ask why."
You're forgetting that Hadida was also the main producer on the first film. Why would he change around his own work? That makes no logical sense whatsoever.
And yes, there is monetary reason to retcon things from the first film: gamers complained that it was different from the game's lore, and bringing it back in would make the more-vocal people happy.
A vocal minority of a game fanbase is not going to make them retcon stuff. That would be silly, because then they would be ignoring the much larger crowd that dropped their money on the first film, just to please a small amount of people. That would actually
lose them money, not make more of it. It would confuse even the casual viewers of the first film, and that would create even
more complaints. There is simply no monetary reason whatsoever to retcon the first film. Not to mention, Sharon's and Alessa's ages are both retconned from 9 to 11, Sharon is suddenly made into a baby kidnapped from her parents, Christabella's relationship to Dahlia is retconned so that Claudia is her sister instead, and the cult is living in the Otherword. None of those retcons have anything at all to do with the games, so why did they do them? That won't please the game fans, it will just confuse everyone who's seen more than 5 minutes of the first movie.
Also, a vocal majority of RE gamers hate the canon of the movies. Hadida produces those, so if retconning to make gamers happy is so important to him, why haven't we seen it happen there?
we have no way of knowing whose part is whose.
We have a pretty good idea of it.
* 3D - Bassett said before the film even came out that the 3D is Hadida's doing, so we know whose fault that is.
* Retcons - Bassett talked about the first film in not so nice terms, and there was no reason for half the retcons to have been added by a producer, so we know who created the retcons.
* Cheap Scares - Debatable. Bassett made a blog posting suggesting he was responsible for the scare style, but then went back and whined that it was everyone else's doing in the commentary.
* Script Length - Debatable. Bassett's script is a bit longer than the final film, however, his commentary about liking short movies suggests he wanted to cut stuff out anyway. And even if you try to blame Hadida for the script length, just look at the stuff he had cut out: Heather and Vincent porking in the hotel, a bunch more retcons, the Otherworld in a modern police station with lots of people (tell me the fans wouldn't have raged over that), Lisa Garland kidnapping a baby for Alessa, more slasher scenery just like the other stuff everyone complains about in the final film. The pacing problems were still there in the script, the unused characters who appeared and died just as quickly are still there. If Hadida was responsible for cutting it, I'd say you still couldn't blame him for the film's pacing problems. About the only thing that is an obvious change made by Hadida that hurt the film was to add Suki.