Eh, I dunno. Perhaps MK is Marth's worse match-up, but I still think it's 60-40. A lot of people don't consider a lot of things.
A) You don't have to swing recklessly to SHZone. SHing UpB and down, and swinging periodically doesn't leave you open to Tornado. It comes out frame 13, giving you plenty of time to counter or Dolphin Slash
B) Marth kills better than MK, and we have gimmicks to kill him with.
C) If you're getting edge-guarded/gimped by MK, you're doing it wrong. MK can give you a hard time with getting off the ledge, but you can do the same to him, and edgeguard him more reliably if he doesn't choose a completely safe option like gliding over or under the stage.
D) Marth can also juggle MK, leran to bait jumps, and to chase with double jumps.
E) Marth's wins the Fair trade. Marth only gets hit by the first attack. Tipper Fair is 12%. 12:3 is pretty good win, considering we don't even take knockback.
F) We aren't used to using it, but we still have the pretty awesome run in and shield option.
Now, truth be told, there are some really broken things MK can do that they don't know yet, but in the current Metagame, I think it's 60:40 MK.
Either way, I'd rather fight 5 MKs then two Snakes with controller slot advantage. I don't lose to Snake often, but a Snake running on basics stands a better chance than MK running on basics IMO. Snake's weight class and kill power are dumb.