Getting Physical STAB ice-type move is good and enough for getting banned from OU, but not more than to get usage in Ubers, due to it's inconsistent BP. The power ranges from 50-125, but not as good as other options like Icicle Crash or Triple Axel.
Regardless, the boost that Kyurem-White got was removal of Primal Groudon and support Arceus formes, especially Arceus-Fairy. These wall it completely, which made it very unviable in USUM AG and Ubers, and also Nat Dex AG.
Kyurem-Black struggles against Necrozma Dusk Mane, and can't deal much damge to Zacian-C. Kyurem-White on the other hand makes them risk coming to Fusion Flare, which deals solid damage and OHKOES Zacian with Fusion Flare.
Kyurem-Black also faces stiff competition from other Dragon dancers, such as Zekrom, Reshiram, Zygarde, etc which have better typing and movepool. As such Kyurem-Black is still bad to use in Ubers and remains lame and can't beat Kyurem-White ever :^)