the "way it was meant to be played" wasn't competitive at all, in terms of how the game was at least balanced from ~09 until now. it's sort of a meaningless semantics argument anyways, because while "what was good before" can be good for statistical purposes, it's all about the most optimal and enjoyable way to play now, which for a competitive queuing system is 6v6, so that's that
no class limits will break immediately with teams that know what they're doing, even if valve thinks "welp, might as well try it out?" I feel like they'll put in class limits of some kind very quickly, since to try and balance around it would result in a wildly different game that takes away from how the classes are balanced (or precisely and intentionally unbalanced, rather)
all weapons will be a bit more interesting to look at long-term, methinks. gunslinger engineer is basically by design a slow-but-obnoxious scout, idk how that'll end up