The big disadvantage that the Yoshi series has is that it doesn't have enough characters, the only Yoshi characters currently so far are Poochy, Kamek, the Yoshi themselves and baby version of Mario characters. This is proven in the Smash Bros series, where the Yoshi series is still stuck with one character, lacking Assist Trophies and items.

Unlike the Mario, Donkey Kong, Wario and many Nintendo franchises, the Yoshi series lacks female representation which is quite upsetting when I think about it.

Having female characters of the Yoshi series will increase representation that could be ported over to the Smash Bros games as well as having more original that are significant to Yoshi himself as well as characters that are associated him such as Kamek and Baby Bowser. In addition, you can even have allow players to play as male character or a female character when playing a Yoshi game.

Here's an unoffical example of a female Yoshi character.

Female Yoshi characters can not only be heroes, but they can also be villains. Throughout the Yoshi series, Bowser (Mario's enemy) and to extention Baby Bowser appear as final bosses and having them appear in that capacity over and over again lacks creativity which is my biggest concern with the Yoshi series.