ZSS vs. MK isn't very bad. I think it's just slightly in Meta Knight's favor. ZSS' biggest asset in the match-up is taht she can't be CP'd very well. She is the only character in the game who can go even with MK on RC for instance. There's no stage he can use to just gay her, and she wins in the air.
ZSS vs. King Dedede is very strongly in ZSS' favor. Between the very easy-to-land chaingrab and how easy he is to juggle and just run away from (and thus camp) any ZSS who knows the match-up should not lose.
Snake is debatable, but it's one of my favorite match-ups. Basically Snake owns ZSS in terms of raw character assets like weight and KO power, but ZSS' agility and moveset kinda own him. It's probably Snake's favor, but no more or less than Meta Knight.
ZSS' biggest problem is that she has to be played perfectly because her moves have static, quick hitboxes, so perfect spacing is 100% vital. One mistake and she gets *****. Her tourney placings are sub par because she has one pro player. PatG, WarpStatus, etc. are good but don't have the placings Nick does.
Nick Riddle is placing well in Florida and despite what people aer saying here, he has been placing in Florida for a very long time. He didn't just suddenly show up and start ****** people, he's been ranked for at least a year and has been getting consistently better. He argues that the way he uses the moves Snakeee abandoned are superior and that the moves aren't bad. There are two sides to every story.
ZSS does not have any unwinnable match-ups, except arguably Falco which most ZSS players agree is not as bad as we once thought. For instance, WarpStatus, a good ZSS in SoCal has beaten DEHF in a tourney at least twice. Pikachu is arguably pretty bad, and there are a few weirdos who hate Olimar.
I know this isn't a ZSS thread but I see a lot of crazy assumptions from people who don't know better, so I wanted to clear some stuff up.