pikachu ***** fox and is easier in the short term BUT
A) meta knight still beats fox solidly too
B) IMO it's more beneficial in the long run to stick with your character, some people like atomsk or NL have had success using a lot of different characters but I think that they are outliers and for most people the experience is very important(I also think how **** those kinds of people could be if they focused on one character more, already top players but they could potentially be even better). I think this is especially true of sword users like MK, your spacing is so important and it's harder to be consistent when you're switching characters all the time IMO
C) pika vs fox being a stupid MU isn't news to fox players, most of them probably have a secondary that they've probably put way more work into than you would with pika. you can go MK on them, but then you have a chance of having to deal with MK vs fox anyway, just as well to learn the MU