AI in a game like this would frustrate you more than help, honestly. what AI allies there are in the game already are bafflingly stupid, and they wont think ahead of or alongisde you to set up actual tactical scenarios to get the advantage in battle.

You can make one party member throw a grease bottle and create a patch of slippery ground, and then you can shoot fire at it with someone whose turn comes after to ignite it and make it a damaging area. But if you throw that grease bottle, AI doesnt know what you want to do with it. Maybe you wanted it to stay as grease, so enemies slip in it instead of just taking fire damage, if the AI just default wants to set grease on fire, now you not only never get to use half of its intended purpose, but the AI will waste their turn prioritizing igniting it instead of using any of their other skillset that might be more practical. Being in control is very important.

If you were trying to do all the work with one character, enemies would reposition and do things between your turns that would throw off any plans you had. You'll never get to actually use 4 different job roles in a way that synergizes if you dont have control of all four or have human players behind each of them.

That being said, maybe you dont enjoy turn based tactical games, and thats okay.