We know problems can be solved faster on a "quantum computer" as the term is defined; we don't know that the version of QM that our reality runs on actually all

We know problems can be solved faster on a "quantum computer" as the term is defined; we don't know that the version of QM that our reality runs on actually allows us to create such a computer, or at least scale it up to a demonstrably (not provably! Demonstrably!) superclassical level. That's what the Quantum Supremacy debate is about.