you see Tera Normal on things like SD Gliscor, which beats most Kyurem sets.
To expand on this; the main set people are worrying about is Sp.Def Swords Dance Gliscor, and that set already beats Kyurem technically via Tera. You Swords dance with Gliscor at the same time as the 1 time Kyurem switch in, and with Tera-Normal Facade you threaten non Specs Kyurem everytime. You do still live Specs Kyurem besides Tera-Dragon Draco Meteor which is fake, but you do take a lot more damage so leveraging Tera on Glisc to kill/heavily damage Specs Kyurem is a bit more complicated.
+2 0 Atk Tera Normal Gliscor Facade (140 BP) vs. 0 HP / 0 Def Kyurem: 315-372 (80.5 - 95.1%) -- guaranteed 2HKO
Basically any chip will make the KO certain and regardless this trade is very good since Gliscor can heal off the Kyurem damage later in exchange for doing 90 to it.
In return the damage Gliscor risk taking from non specs Kyurem is this:
252 SpA Kyurem Ice Beam vs. 244 HP / 228+ SpD Tera Normal Gliscor: 130-154 (36.9 - 43.7%) -- 12.1% chance to 3HKO after Poison Heal
If glisc is creeped for bolt then this is the damage calc:
252 SpA Kyurem Ice Beam vs. 244 HP / 252 SpD Tera Normal Gliscor: 139-165 (39.4 - 46.8%) -- 87.1% chance to 3HKO after Poison Heal
As you can see that damage for Gliscor is pretty marginal once you shave off 12% due to poison heal so its about 24%-31% of damage from non specs, which Specs Kyurem was falling off pretty drastically by the time of the ban due to new hazard stack balances among other issues it had prior already. Also that base 24%-31% is further mitigated by using Protect turns after the first hit...
You could then shift base and say "well Kyurem forces Tera on Gliscor" but Gliscor doesn't mind because the trade is insanely favorable and Gliscor usually want's to Tera-Normal for the Facade boost anyways. I don't think Kyurem is an end all be all answer to Gliscor besides arguably Specs sets but those weren't being used much, nor do they consistently kill even the less Sp.def invested Gliscor spreads. In fact you could 100% argue that the Tera-Normal Gliscor vs Kyurem situation is favorable for Gliscor lol. In my opinion Gliscor was already broken before Kyurem ban but that's a different topic for another day.
252 SpA Choice Specs Kyurem Draco Meteor vs. 244 HP / 252 SpD Tera Normal Gliscor: 301-355 (85.5 - 100.8%) -- 6.3% chance to OHKO