I can now object considering the following:
- The Bubble Bounce was already a thing prior to Adventure, and if you look into Sonic 3 development, it was VERY LIKELY that at some point in Sonic 3's development, the elemental shield abilities were Sonic's main moveset.
- The Thok literally uses a sound from Sonic Adventure and was meant to be a Sonic Adventure-esque Homing Attack. That train of logic doesn't exactly help.
- SRB2 also literally has a shield stomp.
- It's also arguably less out of place than Sonic changing gravity for a split second.
My point was that a stomp/double jump would serve the same role as a grav-switch without being utterly out of place for Sonic.