How the hell does Yoshi have a bad neutral? He has one of the most versatile zoning projectiles in the game and a fair he can space with effectively combined with his excellent air speed. Great mobility options overall, sh air dodge, ridiculous options to pressure shield including dair which annihilates shields and a command grab that gives him free damage, fast CQC options that give him follow-ups, and pretty good out-of-shield with a frame 3 nair. That's just his neutral. With egg frame traps and a powerful up air, Yoshi has one of the best advantaged states in the game. His damage output overall and especially in his punishes is absurd. On top of this, things that are inescapable for other characters are not inescapable for him because he has double jump armor and he will jump out of anything that isn't a true combo, including Mario up tilts (you legit can only get 1), AND he has a frame 3 nair. He can cover below himself with dair, punish things that you **** up underneath him with Yoshi Bomb, and change his momentum all over the place with B-reverse egg tosses and B-reverse/wavebounce Egg Lays. I'm not really sure how any Yoshi thinks that he can't kill either. Hella powerful up smash with great range, up air that is really powerful and can even be true kill comboed out of dthrow starting at ~120% or so, fair dunk that also happens to be really powerful kb wise if you don't sweet spot the spike, super strong bair...heck even your frame 3 nair kills by the edge of the stage at higher percents. This character is oozing top tier potential, I don't think he's overrated at all but rather lacking a solid representative.
There you have it. Most of yoshi's tools are listed in the exhibit above.
Let me preface this by saying, Yoshi isn't underrepresented because people don't like him. He is underrepresented because, frankly:
Yoshi is just a bag of tools
On paper, yes. Yoshi seems to have what it takes to be a top tier character for the reasons above. Looking on smashboards, you are bound to see one of the countless statements effectively saying, "Yoshi is good, but nobody good plays him."
Players want a character that flows. This is why captain falcon is the undisputed most played tournament character. Yoshi, while some of his combos oriented around fair, nair, uptilt, or egg traps seem to drive him as a combo oriented character, many others outclass him in that regard.
Players want a character that hits hard. So maybe you don't immediately pick falcon, zss, sheik, or another combo heavy speedster. Perhaps, you play DK and you want to end stocks at 50 with spikes and put on your shades like dkwill-senpai. Yoshi has some hype, power tools like the fair, smashes, or even d-special. However, again, yoshi doesn't excel there like others who thrive with kill power.
Players want a character that is creative. While I'm not a yoshi player, I have noticed that avid yoshis seem to like their mixups with eggs, combos, read up smashes, perfect pivot uptilts and that great jab. To most other players, there are the duck hunts, the bowser jrs, the warios, and many other choices on the creative/tricky side of smash. These extra crafty people rule out yoshi as an option.
The green dinosaur is just, not good enough at any one category of play, whether it is zoning, combos, killing, setups, reads, edgeguards or neutral to become a popular, tournament staple. Much less, to be played at the
top level. Again, he is just a bag of tools.
Players like characters that win. While he does have lower-high tier status with his tools...
Yoshi isn't winning.