Then who should I drop in favor of either Wyll or a wizard ?
I kinda wanted to romance shadowheart and I felt that a rogue would be nice for scouting.
I've chose to keep Lae'zel simply to add another meatshield. Felt like having only a 2h paladin up front with a rogue in melee would be weak but maybe cleric can get tough enough to tank ?
Personally I think the easiest to get by for a first playthrough without is a thief. I'd just respec Shadowheart to change her stats to higher dexterity and leave strength at 10, but keep her a cleric for story reasons. This way she can open locks and disarm traps, self-buffing with guidance it is enough. She can also scout effectively, using the pass without trace spell.
I tend to not use clerics, and I like Shadowheart as a shadow monk (not the strongest class, but I think it fits her story). Tanking is not guaranteed, many enemies will jump around and get to your weaker party member anyway.
Also, I don't think any role is really necessary, but I think a melee heavy party benefits slightly more from a sorcerer than wizard (Wyll can multiclass into one), because you can cast twinned haste, and this is better than potions.