Personally the only way I see fox winning is if he camps and punishes mistakes with an already established lead. But...at high level play mistakes should barely happen.
Fox's range < metaknight's, and fox's priority is a$$ compared to metaknight's, so I don't see how a fox could even hit an mk at the highest level of play other than a lazer. Also, fox's recovery sucks, and metaknight has 500 jumps so...yeah.
Fox doesn't have an answer to planking (unless the fox player wants to die lol) or air planking (hi plank).
Fox's only kill move is unsafe, unless it pushes the mk onto the ledge from shield pushback, but then mk's on the ledge lol.
So yeah...I think fox gets *****.