Two of the top Melee players (Hungrybox and Armada) use high tier* characters (Jigglypuff and Peach, respectively) and still win tournaments. It's not like you need a 55/45 or 60/40 MU ratio to win games, if you have a 50/50 MU ratio and simply play better you'll likely win. Even if you have a 45:55 MU ratio you could simply win by playing better. If MkLeo is the 3rd or 2nd best player in the world, then he should be able to win games even against hard characters.
I personally think that if Marth is to be top tier, then his current MU charts have to be wrong. A top tier character does not lose that many matchups 40/60 (or 45-55, in Pugwest's case).
Mr.E's MU chart:
https://twitter.com/SS_MrE/status/740988384181637120
Pugwest's MU chart:
https://twitter.com/Pugwest/status/786741022923616257
false's MU chart:
https://twitter.com/fals1fy/status/740923629483986948
If Mr.E's MU chart is correct, then Marth is clearly not top tier (and arguably not even top of high tier). Losing 40:60 to common characters like
is pretty bad, as well as
. Losing 45:55 against
as well as 10 (!) other characters is pretty bad as well. Mr.E's MU chart makes Marth look like a high-mid tier character at best. With that being said, I don't believe it's actually correct, I think Mr.E underrated Marth back then (it's a rather old MU chart, from June).
Pugwest's MU chart has no 40:60 MUs, which is good for Marth. He still loses 45:55 against
and the only top and high tiers he wins against (55:45) are
. Still not quite a top tier.
false's MU chart has two bad 40:60 MUs,
, and five 45:55,
. The only top tier he wins against is
(45:55).
These MU charts would all have to be flawed in order for Marth to be top tier. It would be interesting to see what proponents of Marth as a top tier think this MU chart looks like. If he truly is a top tier then his MU chart needs to back that up.
*According to the 2015 tier list. Perhaps they have moved up to top tier at this point?