CB weavile is at 4% usage, it is not common at all. Yes, it does deinsentives triple axel, that is something that I will give you. However, volc still cannot switch into knock off, the move I would say is more threatening on weavile. Rocky helmet already somewhat deinsentivises triple axel with stuff like corv and lando-t (though lando is in no way surviving). Its a very poor stopgap in my opinion, yes, it resists the move, but it can't truly pivot around it by either applying pressure or getting in a teammate for mostly free.
Lets look at the mons that I said it couldn't beat: these are Valiant, Hatterene, Wellspring, Weavile, Primarina. (I said that kyurem it could potentially beat, but nothing wants to take a draco apart from fairy types)
Valiant: I said before that it beats sets apart from SD, so I'll exclusively talk about sd. It takes a cc, and maybe gets a flame body proc. If it doesn't, what can it do? It can threaten a fiery dance ko which will be devestating. However, if its at +2, valiant will always go for the knock, thats a straight up ko. Now you have to switch to something else, which will have to eat a huge hit and get its item removed. So it doesn't do much.
Hatterene: Volc pivots in, and if it wants to, tera grounds on the nuzzle. If can draw a psyshock, which is something you can easily play around. So there is something that it can do for hatterene.
Wellspring: It has to come in on either a play rough or a power whip. If it gets a flame body proc, then that's cool. It then draws an ivy cudgel, which you have to switch to a water resist. However, the main move it will be clicking is ivy cudgel, so you have to predict them using those moves. Something, but not a whole lot.
Weavile: The best of this list probably. If it switches into triple axel, it has a good chance to get a burn. If it doesn't, then it has to draw a knock off.
Primarina: You are drawing a surf, which while alright, isn't the best pivoting move. Most mons don't want to switch into a surf, for reference rilla takes 46% from it and raging bolt is three hit ko'd. Something, but I don't think that is the best.
So, for all of these, yes, volc does help a bit with them. However, its a poor stop gap. It has to predict correct in order to not get ko'd and then forces these mons into a really devestating move. The only one which is maybe right is hatterene, but hatterene is not much of a big deal.
I get that you are trying to say "it has more defensive utility than you say" but that defensive utility is limited. Again, rocky helmet is literally an item that does the same, but doesn't have to worry about chance.