As someone who mains Yoshi and seconds Mario, I can tell you this, Yoshi has better MUs for sure.
The only MU Mario does significantly better than Yoshi in is against Lucario, where Mario still has a disadvantage. Mario, however, takes the **** from multiple characters like D3, Marth, MK, and G&W as they can wall him to no end and completely hold him out. Yoshi really doesnt have a problem with this as he has ways around walls with his projectiles and superior mobility, but Mario doesnt have the tools to get past characters with far superior range and speed.
Mario also doesnt have ANY advantages outside of a few low tiers, where Yoshi has random advantageous MUs strewn throughout the entire tier list.
Yoshi > Mario, no doubt.