The thing is, a lot of those low tier characters are low-tier because of MK. Without MK, many of them could do much better.
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Wow, you don't know Marth do you?
Marth's fair is a heck of a lot better then MK's, it's safer, has better range, and much more difficult to DI, plus deals more damage generally. (Multi-hit means easier to DI btw)
Also, his nair is amazing, safe on block, and also a kill move, as well as having fair's range.
Uair serves a fundamentally different purpose for Marth then MK. While MK's is probably better overall, Marth's is meant to juggle, and it does that perfectly, MK's combos into itself instead.
Bair is an edgeguard move, and is quite good at it.
Mk a better OOS game? ROLF, LOL, hahahahahahahahahahaha! No.
Marth has frame 4 dancing blade, and is a natural combo, which is an amazing damage racker and can also shield stab, so you're not even safe if you manage to get up shield. He also has dolphin slash which we already talked about, which is invincable until the hitbox comes out, on frame 5. That's ALL he needs. Period. You should also never fail to hit with a dolphin slash btw, counter moves aren't supposed to be safe, they're supposed to be for when your opponent has no chance to block. MK's dsmash is plenty punishable on block anyway.
Marth's OOS game is the best in the game, MK has nothing on him in that regard, it's MK's OFFENSIVE game which sets him apart, because Marth's got defense locked.
As far as in the overall metagame, yes, but that's not strictly true. Strictly Marth has a better defensive game then MK, especially OOS.
The thing is, MK's overall offensive game, and survival abilities more then make up for this, so end result is he's basically a better Marth.
F-smash isn't a very good move overall and is very unsafe.
Marth doesn't generally SHDF because it tends to be unsafe, he's got a great defensive game, that's what he generally uses, using various pokes to force an attack.
One tournament is statistically superfluous.
That said, pro-ban needs to start backing up the claims of MK's dominance with actual evidence.
BTW, Love your sig, that game was awesome.