The camera and the AI pathfinding already struggle with a party of four.
And for that very reason, we can have a bigger party, because the struggle is already a thing and won't change. At least we would have a bigger party to compensate for that. I would be only too happy to accept that trade-off.
I agree with this answer.
For those who’ve tried the mod, though: how interactive are the extra party members? With five companions, for example, can you follow up on quests and/or earn approval for all five while they’re with you?
The only issues i've noticed is that Wyll got stuck with camp dialogue about his father after learning of the kidnapping; his camp dialogue options didn't clear up 'til most of the way through Act 2. Also after the meeting with Gortash, Gale comments on finally getting to Moonrise Towers... Though either of those could just be in game bugs completely unrelated to having Gale, Wyll, Laa'zel, Halsin and Karlach, in the group.