Many of Corrin's moves are functionally distinct from almost any other in Smash. Not just the unique-hitstun-state-boasting pin, the uniquely-double-chargeable projectile, and the only (iirc) smash attack in the game with a hitbox during its charge – but also just a lot of the regular attacks, such as Nair's sheer coverage, Back Air's mobility, Down Air's dragging properties, Up Air's lightweight feel, and etc. If characters were reduced to their hitboxes with no theming whatsoever, Corrin would still stand out.
With theming, of course, Corrin's dragon transformations, chainsaw sword, and even distinctive armor help her stand out even more.
In the context of the original post Lancer quoted (from Autumn), this means that significant development time was put into the character, as opposed to a clone. As a result, Corrin is likely to return to the next game, compared to an expendable clone.
In the context that Lancer seems to be interested in diverting the conversation to, which is more along the lines of a player's perspective, Corrin plays distinctly and adds something of worth to the game on her own merit. No other character plays exactly like her. Corrin's playstyle is vaguely similar to select other characters, but her signature tools shake up her gameplay to the point where it's laughable to suggest that she plays the same as any character we currently have.
also what the heck is that springman comparison lmao
They could've used that time more wisely (such as on the actual game), but they chose not to. Nothing stopping them from using an existing engine or whatnot, I can only imagine.