ACHAP may be too passive, but it is more specific about WHAT alternatives/reforms would be needed.
When I see ACAB, I just think "WHAT kinda reforms are you even wanting?? It just sounds like you are jobist against law enforcement in general". Which I know know isn't the case. But the first impression isn't all that great.
Meanwhile with ACHAP, I think "Ohhhhh! Interesting. I haven't thought about that before. I immediately wanna back you up and reform laws so that police officers don't abuse their power"
I dunno if this is my Autism or not, but I have a higher chance of rallying for Acronyms that are descriptive in their goals, rather than Acronyms that are provocative. This is because I can actually understand their viewpoint immediately from the acronym, rather doing guesswork.