I third the opinion that the classic D&D party is fighter-rogue-wizard-cleric, instead of 2 melee fighters+healer+spellcaster. With a party of 5, the default 5th slot is a bard=buffer/debuffer. Now, usually the rogue is a melee fighter, so in practice we end up with 2 melee fighters. But not necessarily. As thief-Astarion is definitely a melee character, we have all 4 roles regardless.
But yes, currently 3/5 of the companions are spellcasters, 3.5/5 if you make Astarion an Arcane Trickster. And we don't have many of the hybrid classes (Paladin/druid/bard) than can partially fulfill multiple party roles, making party composition more restricted if you want a "balanced party."
Unfortunately, I'd guess that the next companions we'll get are druid and sorcerer, as those are the released classes. Which will make the companions even more caster-dominated (although druid can be a melee frontline via wildshape).
