For what it is worth: I always did find parties of 4 (be it Tyranny, NWN2 or DA:O) too limited. I thought Deadfire’s party of 5+multiclassing worked well, and to be honest when playing BG1&2 I used 5 or 6 companions.
Whenever it is up to actual body count, or character design, I don’t know - afterall most of BG1&2 characters were rather passive.
However, I found party of 4 in D:OS2 far to much. Being being coop game first, there was a lot of tedious stuff to manage - stuff meat into your elf, move heavy stuff with your muscle, scan for dead, use ranger to talk to animals, initiate and reinitiate conversations with different companions, as there is no easy way to take advantage of other characters stats for rolls.
And of course another thing is whenever they want to support 6 player coop.
