I don't know how useless that would have been but in the case of Omnicron it does seem basically useless. I don't know, I don't have studies on hand or anything like that, but when you look at the numbers you have to wonder...

[edit]: maybe some of the more "extreme" (n95 masks, etc) have some decent level of protection, but I'm not sure anybody knows, at least with this variant. Even for previous variants all I've seen so far are models, which as we all know have a lot of assumptions.