I feel sorry for the OP cuz his thread turned into a flame war haha
on the topic of shulk is his side b usable? It feels like yoshi's down b to me
To completely miss the point of your question, Yoshi Bomb is actually pretty darn useful. People tend to not really know not to use it, but when used properly it's a reversal tool AND a kill option. Grounded is especially powerful, and can also be used to put some heavy damage on a player's shield.
...but no, Back Slash isn't useful for much of anything.