fsmash on-shield is without shield stun -23 if it hits with the first hitbox frame. At very high aura (140%+) Lucario does about 7 frames shield stun, you would've to grab perfectly to even get a slightly chance to grab him, fsmash pushes us to far away to grab. Our grab range is extened but so is the time for our grab to reach a decent range. (Yoshis far ranged grab grabs in frame 23 or later)
it's just a human error if they get shield grabbed for it, they could spotdodge on reaction, because they don't expect something like that because getting grabbed out of fsmash against Yoshi is something no one would expect
it's very hard to get an upsmash/uair in if you can't really get under him (and even if you're under him he was options to avoid getting hit).
I prefer platforms because you can punish landing lag on platforms (especially on BF).
it's just a pain to kill Lucario if he's playing safe property. I wished Yoshi had a better killmove