I really don't know, how you come to the conclusion, you need a fighter in the group. Lae'zel is the most underused companion in my games, because I don't need her. I have beaten the game several times with spellcasters and rogues and never had a problem. Gale and Shadowheart are nearly always in my group (and they don't miss often) and then Wyll or Astarion. I don't normally play fighter, so I'm more often than not another spellcaster or a rogue. Works well for me. In fact BG3 might be one of the few games, where I don't feel bad about not having a fighter in the group. Different pkaystyles, I guess.
