It depends on your play style as much as anything.

I play on normal with mods to make things more 5e and less Larian, seldom if ever prebuff as in as soon as you get out of bed, rarely buff at all apart from bardic inspiration - don't even have bless available now. Party is bard, Shadowheart, Lae'zel and Karlach. Modded everyone to have the ability stats I would give their class and recently, on hitting level 8, respecced my bard to b6/sorc 2, Shadowheart is a Tempest domain cleric3/pally 5, Lae'zel straight fighter and Karlach barb7/fighter 1. Can't say if this makes a difference yet as I've only very recently done it. I'm part way into Shar's Gauntlet.
AC is around the 18/19-21 range. Adamantine armour on Lizzie and Shadders. Shadders has the Lathander mace. Lizzie has the gith greatsword from the creche (not the silver thing as I've never seen Voss since Act 1). Bard has Harold Xbow and that's about it for uber gear. I too prefer the old +1 this or +2 gear to Larian's gimmicky nonsense.
My biggest lack up to now has been a decent AOE damage spell and trusty old magic missile.
Most fights are how I like them - winnable if I take care and don't do something stupid. I'm not a big fan of intense micro-management fights (far too lazy for that). If there's a possibility of talking my way out of a mini-boss fight I take it.

I've watched LPs where the guy breezes through fights where I have won but nowhere as easily - I think that is down to them using the vanilla rules whereas I'm modded.