We've had plenty of cases in all gens of legendaries and "legendaries" being unviable in higher tiers.i can't see GF making a very new interesting set of Pokémon essentially obsolete without pairing them with the Dons, mainly because in VGC, the cover legends are usually not allowed until certain rulesets? and VGC doubles is really all they design for
Many UBs sit in lower tiers.
Articuno Galar has dropped to almost unviability.
Calyrex base is unviable anywhere.
Similar situation for VGC, where certain tapus basically never saw play outside of low ladder, most UBs are unviable (basically anything not called Kartana), lot of restricted are terrible since you'd rather use the actually good ones, the galarian birds have seen relatively low usage due to requiring too much support and/or dynamax to work.
As far as VGC goes, some of these mons will still be valid just off bst/movesets.
I do however hope that there's another way to set their field condition until the restricted format.
Well that... or Koraidon/Miraidon won't actually be classified as restricted and will be Tapu-tier instead. I don't expect this one, but I don't 100% exclude it.