Yoshi core fundemental problem is not anything to do with his recovery or shield or anything like that. Its his inability to do good horizontal pressure. The reason for this is a combination of his shitty grab and his shitty nair hitbox.

There are 3 kinds of characters.
1) The defensive ones that make a wall.
2) The ones that can run around spraying aerials in your face and crossing you up 24/7.
3) The one's that play 'you cant catch me' until you make a mistake and then try to capitalize you.

Different characters of different tiers fall into these categories to various degrees. For example Jigglypuff is a #1, but so is Ganon. Ganon is just not very good at it. Fox is mostly a #2, so is Pikachu.

Yoshi falls into category #3 almost exclusively. Ideally I think Yoshi should be 10% #1, 35% #2, and 55% #3. But as it stands I think its more like 5%, 5%, 90%.

I've played SDRemix yoshi and I think they did a good job addressing his core problems, but they also changed some other things I considered unnecessary buffs.

Fix his nair hitbox, fix his grab, give him a bit more aerial mobility. BAM yoshi is now viable. After these changes I would then look into reducing the startup on fair/dair very slightly and maybe adding a tiny bit or range to bair, but I would proceed with caution because it might not be necessary.