You must not have been looking very hard; US Super Turbo was all about counterpicks. It's always been much less popular in Japan, but you were weird if you didn't have at least three characters that you used here.I never seen counterpicking in Street Fighter, Mortal Kombat, Soul Calibur, or Virtual Fighter. Hell, I barley saw any Counterpicking in Melee except for the very Bottom Tier characters.
Yoshi isn't a character that requires Counterpicking for certain characters, because, again, Yoshi has good matchups and doesn't need to.
I'm just a guy who doesn't like Counterpicking in general. Winning is true, but it's not the spirit of it. I would gladly Sacrifice a few wins to stick with my main. It just doesn't seem right just using someone else to cover the weaknesses. I rather just ride it out and play smart, actually learning how to deal with those characters
In general, it would be smart to have a backup character, just to broaden your horizons. Yoshi's matchups obviously aren't that good, or he would be placing a lot better than he does.
I am just as adamant about using the characters I enjoy to succeed. I used Bowser against Marths in Melee, and with enough practice, I won that matchup. Sometimes, it's just plain dumb for someone who wants to win to continue using the same character all the time, but someone will succeed with enough effort, and I wish that person the best. (Hell, I do it, XD.) I was still able to understand that Bowser had it bad against some characters. Honestly, what does Yoshi (Or just about anyone) do against an intelligent Dedede who is under a platform, F-Tilt spamming? It's hard sometimes.