From what I understand, a balanced D&D party needs for archtypes: A melee fighter for dealing with other melee fighters, a rogue for detecting and removing traps and locks, a caster for dealing with enemy casters, and a healer to keep everyone standing.
A party limit of four really completely kills gameplay diversity in my mind. Are there any good multiclasses you can do with a level limit of 10 that can let a character handle two of those roles without crippling themselves at one of them?
I actually think the reduced party limit provides an interesting challenge for party diversification. For example, a bard can act as a healer and a caster, taking up two slots. Any character can be given a single class of rogue and function just fine as trap/lock utility. But the thing is, I haven't seen anything to indicate the conventional balanced party is completely a necessity.
So, you could do something like:
Paladin - Tank, support healer, buffer
Eldritch Knight Fighter - Melee with ranged magic damage
College of Lore Bard - Healer and magic control
1 Rogue / 9 Pact of the Blade Warlock - Traps/Locks, sneaky magic melee
Or, something like:
5 Four Elements Monk / 5 Dragon Sorcerer - High mobility melee damage with some magic ranged options
4 Pact of Vengeance Paladin / 6 Way of Shadows Monk - High mobility melee damage
6 Battle Master Fighter / 4 Assassin Rogue - Long range damage
1 Rogue / 9 Trickery Domain Cleric - Healing, support, traps/locks
That last option is a party I am planning as an all drow group assassin group.
So there are a wealth of options out there. No need to box oneself in by going for the most balanced party build. In my first playthrough of BG1 my part was Fighter Bhaalspawn, Imoen, Kivan, Yeslick, Viconia, Branwen. A fighter, a thief, a ranger, a fighter/cleric, and 2 clerics, and not a wizard among the lot of them. Worked out just fine. I am confident BG3 will be designed in such a way that you can get through with aberrant builds.
