Your argument is incredibly weak if you can't provide examples. You can't just throw a random figure out with no specific match ups (especially if the figure is made up) and expect people to say you're right. MK doesn't affect matchups that aren't MK. MK can't start controlling things that balance other characters in match ups MK isn't even in.
ok! i'm at home now, so ill do some examples. although before i do, a quick mention that mk does influence mus that he's not participating in, because he quite easily controls which characters can actually get through the bracket. only characters that have reasonable mk mus will make it through (unless the play is extra amazing).
examples that im very comfortable declaring (although there are obviously personal preferences, these are definite trends):
Snake
vs. MK
FD, BF, SV, YI, PS1 - played on SV
BF, SV, YI, PS1, LC - played on PS1 (preferable for mk)
vs. Diddy Kong
FD, BF, SV, YI, PS1 - played on BF
BF, SV, YI, PS1, LC - played on BF (uneffected)
vs. Marth
FD, BF, SV, YI, PS1 - played on PS1
BF, SV, YI, PS1, LC - played on LC/PS1 (personal preference)
vs. Wario
FD, BF, SV, YI, PS1 - played on PS1
BF, SV, YI, PS1, LC - played on PS1 (uneffected)
vs. Ice climbers
FD, BF, SV, YI, PS1 - played on SV
BF, SV, YI, PS1, LC - played on SV (uneffected)
vs. Pit
FD, BF, SV, YI, PS1 - played on BF
BF, SV, YI, PS1, LC - played on BF (uneffected)
vs. Dedede
FD, BF, SV, YI, PS1 - played on PS1/BF
BF, SV, YI, PS1, LC - played on PS1/BF (uneffected)
Ice Climbers
vs. MK
FD, BF, SV, YI, PS1 - played on YI
BF, SV, YI, PS1, LC - played on SV (preferable for mk)
vs. Diddy Kong
FD, BF, SV, YI, PS1 - played on FD/SV
BF, SV, YI, PS1, LC - played on SV (largely uneffected)
vs. Marth
FD, BF, SV, YI, PS1 - played on SV
BF, SV, YI, PS1, LC - played on SV (uneffected)
vs. Wario
FD, BF, SV, YI, PS1 - played on BF/SV
BF, SV, YI, PS1, LC - played on BF/SV (uneffected)
vs. Snake
FD, BF, SV, YI, PS1 - played on SV
BF, SV, YI, PS1, LC - played on SV (uneffected)
vs. Pit
FD, BF, SV, YI, PS1 - played on FD/BF
BF, SV, YI, PS1, LC - played on BF (largely uneffected)
vs. Dedede
FD, BF, SV, YI, PS1 - played on BF/SV
BF, SV, YI, PS1, LC - played on BF/SV (uneffected)
Shall I keep going? As demonstrated, the only mu actually affected was the MK mu, where MK gained a slight advantage. Safe to assume this happens in other mus also.