This just about learning how the AI works:
Save before encounter. Try out things. Consider it like a chess game, think this way "how will the AI react if I do this?" (and run a few tests, every encounter, until the pattern becomes clear)
Reload save and now do it differently: sneak a wizard in a good spot and keep hidden, if gets revealed try again and pick another spot, high ground is best; move the rest in good position as well, then start the fight with a sneak attack from your fighter (which is tanky, can self-recover health once and can survive being focused), then after attack starts switch to the others and do something with each. If went well make a new manual save.
Then reload again and try a different approach. Just to study what the AI does. Learn what works and what not, how can the fight be made very easy and have can lose it or barely survive it.
I agree that many things need changed & improved.
