I was wondering if someone was going to point that out lol. Yes, it would make Assault on Arkham and the prequel Arkham Knight comics non canon unfortunately. Speaking of how King Shark and Boomerang died. It sucks though because I loved the story so far that has been told within the Arkhamverse so unless a BIG explanation comes along then as of we know it the continuity is shifting.
Deadshot (the one we knew from origins, AOA, and city) on the other hand is being heavily implied that he was an imposter and this game will be showing us who the real Floyd Lawton is. I don’t mind it, but at the same time it felt pointless to do it. We’ve already bonded with the other Deadshot which was worthy of the mantle and has already squared off multiple times against Batman so for him to be called an “imposter” just doesn’t feel right.
When I first saw this game it didn’t feel like it was connected to the Arkhamverse in general so yes I agree it should be a standalone universe, but I suppose they aren’t going that route. Despite Arkham Knight wrapping it up nicely, there was a sequel that would be following Damian Wayne as Batman set 10 years after, but it was scrapped and replaced with the Suicide Squad game.