I can admit this much, even though I do not think the game would be better off if CCing were altogether removed or even changed in this particular game, the mechanic could still be implemented better. For consistency's sake I'd rather it didn't change In PM, but if I had to learn a new game or relearn smash, I'd rather the mechanic existed In an improved state.
The effects of it could be scaling. Rather than a flat 4, 5, or 6, frame landing lag depending on the receiving character's empty landing IASA, it would work better as a flat reduction to hitstun time upon successful standing landing. Say, 20 frames. If the move applies less knockback than what's needed for the full 20 frames, the character receives no lag and can retaliate instantly. Anymore, they receive the difference, causing a scaling effect in the effectiveness of CCing, up to 11 frames of lag. After 31 frames, it's ineffective of course because 32 frames is the knockback threshold for knockdown. Alternatively, and probably better, is a multiplier reducing hitstun if the defender is not knocked down. It's different from real CCing (2/3 KB while in crouch animation) in that it only applies if you stay grounded on your feet, but has the same ability to be available at any time. It's even got scenario specific draw backs, such as keeping you grounded and available to moves more effective against grounded opponents in situations when you still aren't reducing hitstun enough to punish, meaning it's not always the best idea to ASDI-down CC certain attacks even if it's possible to do so without being knocked down. It's still not entirely intuitive nor is it perfect, but it's much better than a binary system.