Open / Closed weapons were just a beta thing. Previous games (other than 2042) have had class locked weapons, with BF1 having entirely unique primaries, side arms, and gadgets, as well as very recognizable class character models.
I imagine that their data shows no significant difference in class diversity whether assault rifles were limited to assault. The support class was incredibly over powered, particularly on maps / modes without vehicles, and otherwise engineer was the only other useful class. You could have had support go without a weapon for as much as it seemed like some players were running around only reviving, especially with how ludicrously strong the defibs are both for instantly reviving entire squads, and shotgunning enemies in close quarters.