On Kamek - first things first, he's plainly just a Mario character these days. Not a Yoshi character. I understand why people still associate him with Yoshi, but I think it feels kind of forced nowadays to consider him a "Yoshi rep" when the character has been so prominent in the core Mario brand for the last several years.
As others have mentioned - pretty much since New Super Mario Bros Wii, with progressively further and further measures to establish Kamek into even more of an individual. RPGs such as post-Sticker Star Paper Mario and a recent example in M&L Brothership give Kamek prominent roles, he has become a major player and host in Mario Party. Perhaps even most notably, a central role in the Mario Movie as Bowser's most trusted advisor. It's been kind of a quiet climb, but I think it's safe to actually consider Kamek one of the more active players across the Mario brand.
With all that in mind, Kamek actually makes a really strong case for himself. And gameplay wise, I think there's a lot to be done with more of a toony wizard / witch type moveset the likes of which we haven't really seen yet. Mages remain a surprisingly underexplored archetype in Smash and I think Kamek has a lot to offer, and has quietly joined the ranks of the most omnipresent Mario characters of the modern age. He might not be my top choice for a new Mario character, but it's hard to argue with his credentials when you lay it all out.