You're blaming AI, while you should blame game mechanics.
1) Tanks break away when they are shot, to return fire. They tend to ignore ranged defeders shooting though (probably something to do with reacting towards defenders in range only). Shooters do that too, except (and here's the bug) when the defender is near death, then they for some reason ignore that defender unless it's reacting to getting shot at.
2) When howitzers destroy their first target, they scan the area around and target the next first closest target. Even if to get in range to that target they need to cross a maze or break off behind 2 corners, that building was physically closest at the time when they destroyed the last building. It's not a bug, the game's targeting system was DESIGNED that way and this can't be fixed except for rehauling the entire targeting and AI system (won't happen)
3) When planes' target has been destroyed, they take the next closest target to the FIRST target (where the plane is, doesn't matter). During that time, they will do the spin manouver (even while doing the spin manouver for the original target) to line up the shot, and that will get them flying over the map. If, god forbid, it targets defenders that are already getting killed, it will continue doing spin manouvers across the whole map. Again this is by DESIGN, no bugs here.
The game AI is simple because that's what they needed, a simple targetting AI that isn't too taxing on people's devices. Not a lot of effort, and people with budget devices get to play, not high-end gaming phones only.