Would wager a lot of the motivation for having the slowdown and posing is to lessen the gap between veterans and inexperienced players. In terms of mixups, all the slowdown/posing does is inform everyone that a mixup is about to happen. Like, how many noobs have been destroyed by haircar FRC? The XX series has been around for 10+ years. Old and new will be fighting each other and that experience gap has to be reconciled some how, otherwise GG ends up right back to where we left off.
Better than ultra combos.