I don't think it is top tier. I would at least put things like Fire/kin and Elec/kin in that tier for the sake of synergy. Yes, I get Fire/kin is way in the lead as a favorite, but for the sake of synergy both play in melee with auras and Elec has -end which can be used with Transference. Kin is by default better in teams. It works better with controllers since they get pets and mitigation, but Grav's pet is more known for adding control than offense. The added mitigation is welcome to a Kin. Hopefully any KB doesn't create too many issues.
Saying that, I think it's fine as a combo. Grav does solid damage. Boosting that is a good thing. Wormhole can be super helpful at times for positioning which matters to a Kin. Having more ranged attacks isn't that much of an issue considering I took a Kin/sonic to 50 on Live. You don't have to have auras or PBAoEs to be in melee. 😁 You can also hang back enough and get close as needed, again, see Kin/sonic. I probably mix/max a bit too hard to roll one, but I have thought about it, and I think the powers would work well enough together theme wise. Grab Fly/Hover and rain objects from above. 😂