The issue (already mentioned several times in this thread, I assume) is that a party of four somewhat locks your party composition choice. You need a frontline, a buffer/healer, an arcane caster and then you have a free slot.
So you generally have to choose between bard/rogue/warlock or any niche spec. Having a party of 5+, on the other hand, grants you way more freedom and nuance in your party composition.
Oh well, I suppose it's too late now, Larian did not listened/delivered on this matter in a two years, I seriously doubt they will in the next couple of months.
I would argue that DnD5e is very lax with party composition, plenty of folks did just fine with an atypical or homogeneous team. I have seen a 4 paladins run or even solo runs go through just fine. Multiple classes fit the archetypes you described if shoehorning your party members into strict roles is your thing, so that leaves plenty of room for freedom of choice.