(I refer to it that way rather than a "variant" because Quantum Immortality should always be parameterized by an acceptance function... for any given acceptance function, that function will be preserved in the quantum multiverse, and scoping the precision of the function affects the percentage of universes that retain it rather than whether it will be retained. There's actually nothing in that definition that requires that the acceptance function describe a "conscious system", you can stick something that accepts a "civilization" in there just as easily. Or "this rock over here". Or any other thing you like. Conscious systems are just a particularly interesting case to us conscious systems.)
It's not a vacuous argument, though it is a funky one with very odd characteristics. But if you accept the suppositions underneath it, it does follow and is not vacuous. The suppositions are certainly not completely obviously true on their own terms, though.