It is not appropriate to compare the two metas with each other. Nat Dex is an entirely different metagame that is shaped completely different than OU, as NatDex offers Z moves, Megas, every other Pokemon that isn't available in OU, and the removed moves. Why it is not banned here is that common defensive Pokemon such as Mandibuzz and Toxapex does a good job at handling Urshifu, while it is also possible to revenge kill it with faster Pokemon such as Unburden Hawlucha, Rillaboom, Alakazam, etc. Overall its not a ridiculously powerful Pokemon.