Does the game use Lua or a scripting language for the AI? If not, I think that would easily explain the problems, as it seems like so much behavior of the NPCs was never iterated on.
So I don't mind breaking out the monowire and fucking up every single one of them - even MaxTac - until they give up. Which is also funny... lop the heads off about 8 patrol officers and 4 MaxTac enforcers, and the cops get the message.
Driver AI? Let's just assign them a route to follow to see how it looks, we'll worry about real AI later.
Police AI? Just give them gang member AI (shot on site, aggressive when looking at them) until we can do a better pass.
Wanted System? Just spawn in mobs to something happens when the player gets a wanted star. We'll sort the real system when Driver AI and Police AI is finished.
Etc. Etc.