I agree with all of this, I don't like Larian's insistence on putting time and focus on origin character content in a CRPG, that seems backwards to me.
But then again I'm someone who grew up on the Troika RPGs instead of BG1/2, where their games were much more focused on reacting to you the player and your choices, and much much less so on the companions, if you even had any.

I am currently doing a 4 character custom party via the 4 instances work-around, it's been very fun, but the game definitely doesn't expect you to play that way.
Most origin characters still insist on joining you and don't check your party size until you acquiesce and say "Fine, you can join" which leads them to be like "Oh no you need to get rid of people." and it comes off as very weird with mixed signals.

I also find that custom characters don't interact as much as they did in DoS2, you could have two custom characters react to eachother in dialogue when making choices (Not all the time, but for certain occasions). They will occasionally make random comments in the over world that *seem* to be in response to one another but it's very vague.

Anyway I'm getting into the reeds, I would much rather be able to have 3 hirelings that I have total customized control over than to have to do the 4 instances nonsense, or be made to use origin characters. I don't know yet how well or poorly BG3 works with smaller parties, we have no Lone Wolf mode despite the fact the game's story feels best with a party of 2 in co-op.