That's what the term "vassal state" means. It doesn't "deny statehood", technically. What it indicates is that in practical terms, a state (or the regime running it) can become so dependent on the resources of a superior state (indeed owing its very existence to it) -- that it is fair to say that it is independent in name only.

Which pretty much describes the relationship of Belarus vis-a-vis Russia, after the events of 2020.