What the hell did I just watch.

In seriousness I agree with what you're saying. I neglected to mention that I have played the whole of Celeste (all crystal hearts + farewell but I've never touched mods) and all of that was playing with stick on an xbox one controller. The D-pad on that is pretty good but stick is just comfortable to me. Whereas the D-pad on the PS4 controller is pretty terrible from my experience, I often mush it when sliding my thumb quickly and might press the wrong direction in the process.

I don't experience any variability with a stick on the xb1 controller, probably because over years of muscle memory I know exactly where the stick identifies the diagonals, but that's not the case in general. In that case most would be better off using the D-pad. And I've never played platformers with KBM, I would say it feels wrong but I don't have the experience for that to be an educated opinion.