See, people keep saying this, and initially I myself bought into it, but now that I have had the chance to actually play 5e myself, through a lot of Solasta but also a lot of virtual-TT play of 5e, I strongly disagree with this. At a minimum you MUST have a dedicated healer with lots of healing or else you stand to have most if not all of your (small 4-person) party go down during a battle. And rests don't help with respect to keeping your party alive DURING a battle.
In BG3 there are lots of healing potions you can use during battles. I never min-max and just select the companions I want. 😊 An all caster party works great as well!
