>>29539722Odds are it's going to be top of UU, as others have mentioned, it's likely Tapu Fini will outclass it with legendary stats pushing it out of OU. The only way it's out competing it is if Primarina gets a massively better HA or movepool.
>>29539862The terrains are about as relevant as Sand. If you have room to pack Excadrill and abuse it, great. If you don't, it really doesn't matter, you're using Tyranitar or Hippowdon for how they contribute to your team, not for Sand Stream.
Running multiple Tapus together isn't tremendously likely anyways due to relatively mediocre type synergy (Koko/Fini + Bulu is ok, but nothing to write home about) so that's not really a major consideration to deal with. If anything, having multiple terrain control might be STRONGER than only having one, not weaker.
>>29539997This is also a possibility. Primarina is almost certainly finding itself in OU if Fini gets banned.