Maybe I suck at building companions, but I'm struggling with most of them
Paladin is both tank/damager, early game it's easier to run her with 2 hander, until you find better equipment. due to paladin smite and later mass smite obviously op. she can also multiclass into many things, if you don't like paladinos.
Lann is op, and can be op cleric (druid) multiclass with bow, ac from wis, all that, + pet
Wenduag is make-your-own op fighta char.
Ember is the OPest, if you know what "a re-roll" means. Pick abilities that suck enemies for -to everything, cackle, and abilities that force re-rolls (or give you re-rolls). Witch is basically a -1 diffiiculty level if you have someone to use their -saving throws.
Camelia is support buffer and they say a tank if you pick tank shaman stuff. oh right, also debufs. I usually don't play her but I once just switched her into elven curve blade damager with sneaks. I also seen some ppl switch her into ranger and I ran her as hunter with dogi once.
Tiefling is flat minmaxed thief/mage, an absolute no-brain.
Lestat made by russian 40+ yo fangirls who watched too much vampire interview on old russian television is an obvious blaster (sorcerer casting + cleric dmg+cc anti chaos spells), for some reason owlcats shoved him into healbot build tho. not sure what his extra powers now are, since he was bugged in beta, but he can spam lots of spells, use it.
Neni struggles a lot like all mages early, but basically she is for a party that can buff casters and cc and kill with Illusions. early game use her to multiply all scrolls and teach them to Neeshka-man. since I play casters I prefer to multi her into something tho to replace Neeshka-man.
Sosiel is just op, it's like a muscle blacklord tristian.
Regill is straight no nonsense dual, since many attaxx, you need to add to every attaxx extra damage (crusaders edge, hurr). he uses Crushing weapon because, right after you get him, Owlcats throw crushing-vulnerable swarms on u wink wunk hint hint
Dorf is banal axe killer
Primadonna is just flat OP ranged obliterator.
mythic/secret companionz not gonna go into them, haven't met all of dem.
problems I see with chars is weird ember build (although might work later with items), strange spells for Cam, and since you already have heal supports in Cam, Ember, and later Sos, Lestat feats are pointless.
At the same time there is a lack of alchemist equivalents with elemental dmg.
Aside from that I don't know how losing with these minmaxed shits (who of course also get various DM-approved companion itemz) is even possible. You want a harder game, roll mercenaries. I always multiclass companions into some dumb shit to get a more interesting game cause of braindead effectiviness of chars like Lann "multi log thrower" etc.