that's... not how it works. it depends on who is using it. a Pokémon being in a higher tier doesn't mean it's bad for a lower tier to have it, it just means people in said higher tier use it a lotNononono... He's not so broken in PU.
*PUBL
Not very so broken...
My opinions: Virizium could move from ZU to PU. Porygon2 could move from ZU to PU. Dragalgue could move from NU to PU