4 is a good size for tabletop.
Yeah, but a tabletop session and a CRPG are two vastly different beasts.
For one, in the first 4 is the "suggested" default number of players because realistically speaking gathering more on an regular basis becomes a pain in the ass.. Still, most big and well structured campaigns allow and support for more (it's not a coincidence that Critical Role, arguably a big part of what popularized D&D to the masses these days, is played by a party of 6+ actors).
That aside, in a CRPG you won't have the luxury of having every single character created, curated and acted by a human player, so offering a large cast and the possibility to carry many of them around simply opens to more dialogues and sidequest options, interactions beween characters, banters, etc.
The idea that having just four and (even worse, if they stick to what initially suggest) force the players to "commit to their choice" at some point sounds incredibly limiting.
But frankly my main issue with this on a personal level is that I just find the party compositions offered by larger group WAY more compelling than sticking to have a "perfectly functional" 4-men party that leaves no room for significant variety.
Also, bonus argument for loot: having a larger party with more differentiated roles leave you a lot more chances to put a large variety of unique loot to good use.