The thing about hitting someone's shield with the last frame of the hitbox is that since shields expand much further than the character's hurtbox, hitting a shield with the last frame of a hitbox would require you to actually misspace your aerial.
This is kinda the standard for high level spacing in general, space for shield which also accounts for most characters movement animations when acting that you cannot react to, clutch/notice react to not shield and maneuver forward if necessary. If you're potent at spacing like this, people are going to struggle even if you do whiff them as it's requires a read more so than something you can react to.
Marth's neutral air (still good for this) kinda gives you the idea, I coined it back in Brawl as the carrot and stick (something something horse) analogy:
Marth's first hit of neutral air is shorter range than his second hit.
If you space for the first hit on shield you're also covering people expanding closer, being at the right spacing and retreating around the first hit is exceptionally safe (to the opponent it's the carrot). If you don't power shield (even if you do...) the first hit you cannot do any attack before the second hit will come out, this protects him (this is the stick).
If the first hit connects, even if you're retreating you'll still find yourself landing the tipper on the second hit, if they shield drop poorly or don't shield then the second hit exists to cover that space between them. It also strikes a third time, at slightly longer range, and this hit would kill MK centre stage at like 80% (110% with perfect DI/momentum cancelling) back in Brawl so it was super risky to challenge it.
I only ever fought three players who knew how to deal with this properly (over just respecting it) in the Brawl era: Tyrant, Mew2King and Ramin (i.e. all better Marth players than I). The main difference now is that it doesn't auto cancel 3 frames after the hitbox ends (which timed well to a shff!), it can't be + on shields anymore :<