Similarly (to be fair), people arguing FOR a party size of 6 shouldn't be using arguments such as "a 6 person party matches BG1&2" because similarities don't necessarily equal better. 5e != AD&D 2e.
Well, then again the preference for one type of party setting over the other have very little to do (if anything at all) with the specific ruleset used.
A party of 6 worked great in BG2 because it was an ideal compromise for this type of computer game, not because something about the AD&D is "specifically tailored for that type of party". Which is also what makes the argument "Bu-but the PHB/DM guide suggests 4 players" is bloody stupid. And not just because 4 players are suggested as a BASELINE rather than a top ideal, but because that has little bearing in how you play this type of computer game.
It's the same reason that years ago made a lot of people complain that a party of 4 in Dragon Age Origins was obviously a dumbing down of the formula tailored around console players. And this is despise the fact that Dragon Age was a ruleset with THREE BLOODY playable classes.