cod 1 ai literally have aimbot bro (i saw it in a video they literally track to the player) but idk about their cover skill tho seem kinda bad to me (they run to stand in front of me when i hide lol)
Enlisted bots also have aimbot but got nerfed to being almost worthless in most situations.
it could easily be dev overload. if programmers are constantly switched to different problems instead of focusing on one problem in depth, they will always suck at solving that specific problem. programming requires lots of research to solve problems better/faster.
problem is that number of skilled players who find bots boring is small in number. lots of player perform on par with bots or even worse than them.
it already works like that. it is just that you also have reset mechanism(just duck behind cover and aggro resets). used that mechanism to farm ~150 kills with one soldiers.
well i can easily explain this. if DF is learning from playerbase then it is SISO problem (shit in, shit out). 
making AI is extremely easy for simple game. you have aggro table, you have ai decision tree and for cover you can just use cached table with nav coordinates that could be even entered manually (you could even script every bot manually). problem starts when you start doing big maps, specially with destroyable elements where you cant cheat with manual tables, there are multiple enemies from which you can seek cover from multiple direction etc.
also look at this from ex fallout dev:
programmers nowadays overestimate their estimation for even simplest things.