I think yoshi will be higher than mid tier tbh as the metagame progresses. It might be a stretch but I think if a player played a perfect yoshi match I think he could be low high.
Anyways, give it more time. I think we really are spreading awareness about how good yoshi can be. Even though I'm not all that great at him, I still beat /a lot/ of people when I'm in the zone and playing correctly and everyone always gives me a 'WOW I never seen anything like this' impression.
"Yoshi mains: Slowly changing opinions since 2008." <== should be our tagline hahaha