Nonsense. The start of the fight was great, they only lost the plot in the last episode. Amou going on a killing spree can be explained with her seeing how Nomura was gaining the five swords as allies and to take them out before they all could gang up on her (which would be better than just jealousy), but the bitch was beating up people for less in the past and likes to lick blood from her hands, so there really doesn't need to be much motive.
Blind loli being weak was mentioned earlier, though that particular scene was indeed a bit ????. It had to be, though. I don't see any other way to dramaturgically solve that, though, and it's absolute standard. At least she kept standing and started to attack again when Nomura interfered, so there's that.
The flashbacks were absolutely necessary for Nomura and Amou's backstory, you can't honestly expect the whole basis for their conflict to be omitted?
Amou falling for MC out of love was shit, but again, only in the last episode. Her craving confrontation to feel pain (an experience she obviously can't have anymore) makes sense, and if they had left it ambiguous, it would've been better.
It's also very confusing how you keep saying only desperate yanderefags would see her as an antagonist, I'm under the complete opposite impression, that it's desperate yanderefags who try to redeem a clear antagonist. It's baffling how anyone could think she's not.