Hovering is something I DEFINITELY would love to see. Other than that, I concur with the other two points as well;I think his problems could be answered with a few potential options.
1. The ability to have more than one Mecha-Koopa present on the battlefield, allowing Jr. to zone as he was meant to. An opponent can't answer to two of them as easily as he can one; the reason for this being that unlike Diddy's banana, Mecha-Koopas walk toward your enemy, making it a facile task to simply stand idle and press a or dash attack into them at the right time. A banana is stationary, forcing the enemy to come to it, allowing for superior, less fallible set-ups.
or
2. Mecha-Koopas cannot be picked up by enemies. This is self-explanatory as far as utility is concerned.
or
3. Bowser Jr. can hover. He's riding in a clown car for pity's sake, why not have him hover like Peach does on his second jump?
more mecha-koopas = more pressure
My Lemmy is usually pretty good in battle, but some characters can just hit me too hard with my own koopas.