Yeah RE was never that serious about biology etc, BUT
I really really hate how decided to handle the mutagen element of the game. Las Plagas were a nice side trip, ok, but anthing after that simply went downhill (not counting t-Abyss).
Tiny plagas can now mutate you into Leviathans; Oroboros doesn't which makes no sense at all (except for Reapers, those things are hilarious); C-Virus which apparently can do anything at no downside.
First of all, we need the Tyrant back. Simple as that. Scale down the size of monsters we get to face. A human reporposed as killing machine is much more scarier than a centaur/dino/human/giant fly hybrid that can talk.
Also let us fight monsters, not humans with superpowers. Other than Wesker ,I got that feeling from the J'varo, who where more or less humans with the nice benefit of gaining superpowers when wounded.
TLDR; Give us back good enemies.