As others have said longshot has a nerf coming his way, so you can either enjoy his awesomeness now and deal with possibly being stuck with a nerfed version of him or rank domino and if he stays amazing then rank him later
Longshot is untested waters. He seems flashy but the only gameplay we have seen is in Act 4, RoL and arguably the easiest path in 6.3 that can be destroyed by vast majority of top mystics. Domino is already a proven champ and longshot is way overhyped with not much substance imo until we get more endgame gameplay.
Comments
I agree. He's a prime target for a re-balance down the road while Domino has already gone through a few re-balances at the start of her run already.