if metagross gets banned there wont be any real counter to Tapu Lele, Tapu Lele on the other hand just makes metagross even stronger with psychic terrain. Greninja keeps metagross in check, and Greninja im sure gets used a lot more than metagross. Though I think if metagross gets banned a lot of people are going to use bisharp to counter Tapu Lele.
If you really cant beat metagross, just use mega scizor, or Greninja, or both.
If you really cant beat metagross, just use mega scizor, or Greninja, or both.