I do think an optimally-played Peach should beat Diddy, for what it's worth. Like KID I remember KOS-MOS just never, ever lost to Diddy Kong.
Interesting that MK is listed as -3. I thought most good Peach players said it was a little better than that, but hard to remember.
And Peach vs. ZSS is probably a very slight advantage for ZSS at high levels of play if only because ZSS should be really hard for her to kill. The first 70% of the Peach match-up is really frustrating though, ZSS sucks out of shield vs Peach, she just does not care if you shield something. You have to play really smart and abuse your dash speed and try really hard to never hit L or R, or you get locked into forward roll as your only actual option. Having it listed as 0 isn't an egregious error. From a certain perspective it's pretty even.
I think the ZSS figures are pretty correct by the way, although I think Snake is 0, TL is +1, Pit is +1, and Kirby is +2. I also don't see how ZSS ever wins the Diddy match-up. I think ADHD could beat basically any ZSS with one hand on the controller. >_>