I think its more about the vast disparity between player skill in the same rank.
I can only speak for myself here, but im playing my way through emerald right now, and im getting matched with anything between plat 1 and emerald 1. And if emerald 4 is equal to gold 1 from last season, and emerald 1 is equal to d4 from last season then you can see why the rank would be a shitshow.
Although so far i havent really noticed much of a difference between player skill myself. Everyone is equally bad or good, some just have good or bad games.
As someone already said its still too early to tell if the skill difference between emerald 4 and 1 is going to be as big as its expected, but if it really is that big then we're back to the old diamond clownshow. Where difference between d5 and d2 were so big it felt like you went from bot games to pro play.