Trifroze
all is cheese, all is jank
It's common knowledge that ZSS' neutral is awkward and hindered vs short characters, but it should also be common knowledge that ZSS decimates lightweight characters with her bnb. Pikachu has a particularly large tumble hurtbox as well because of his tail.I thought Pikachu beating Zero Suit solidly was commonly accepted knowledge, but I guess it isn't. Evidence: when they played Zero Suit vs Pikachu, ESAM kind of wrecked Nairo. So much that Nairo didn't even TRY Zero Suit vs Pikachu when they played at MLG. The simple logic is that Zero Suit struggles vs short characters, which I hope is well-understood enough that I don't need to explain. The thing that really clinches it though is that Zero Suit's out-of-shield is not that great, so she will struggle vs Quick Attack pressure, which Pikachu can really abuse. The matchup is like 60:40 in Pikachu's favor or maybe even a little bit more.
Nickriddle almost beat Esam at MLG if you want to refer to results. It was literally as close as it can be, if flip kick connected from a few pixels further away that would've been it, but it didn't so ZSS didn't get the meteor hitbox, and even then the red sparks showed up so it was a matter of a few percents.
Pikachu probably beats ZSS just because the neutral game is pretty considerably skewed in Pikachu's favor due to character specific attributes, but ZSS' good disadvantage avoids one of Pikachu's main strengths for a large part. Pikachu is a heavy commitment character as well and doesn't want to get grabbed or out of shield up b'd.
I think this matchup is just really hard, but not necessarily bad. There's a difference, since a bad matchup is something where you lack options and/or reward compared to the opponent, but a hard matchup can still be tied or even advantageous. A hard matchup, by itself, only means that while you can have equal tools and reward to the opposing character, it's tough to utilize your tools because they require precise timing and spacing. ZSS aerials are one such thing vs short characters and animations.