To be fair, it does indeed need a buff. The problem that the shield has is that this requires such a significant combo to work even generally well, and the combo is very fragile, and not always enough even when successful, especially non-upgraded. I think that it either needs +1 DR for general usability, or cost 3|2. I support a Gravity effect that removes airborne and that stuff, but that just does not fit a shield. Shields either reduce damage from attacks, inflict a retaliation effect on damaging creatures, or other defensive ability like Reflective. To remove airborne from creatures is not (directly) a defensive measure and therefore does not fit as a shield effect.