As much as I like slime and what not.
Square Enix has been so bold to say Dragon Quest is dead in the west.
Final Fantasy has always been the more dominant, more iconic series.
And let's face it...
Black Mage despite "just being a class," is still a very iconic design for the series no matter how they alter it game to game.
And given that we got classic
&
and
most based on SF2, I feel like Nintendo would push a FF character from 1-6 (who has appeared in two Mario sports games at this point) than, say, Cloud.
I just feel like of Square Enix's series, Final Fantasy really can't be argued to be anything less than the single largest one.
Of them, Black Mage has been used if not as a direct class, then by giving the classic design a cameo in the game or hell even DLC costumes in the case of one of 13's sequels.
Bravely Default, aka "We don't want to CALL this Final Fantasy but it's Final Fantasy" even uses this as a staple.
A long-running, iconic FF character/design going back to the NES days and being used up to FF14 and Bravely Second (hell, Nobou Uematsu NAMED HIS BAND AFTER THEM) and had a playable role in some Mario titles? Seems like a good pick to me.