It isn't even clear whether the class of problems quantum computers can efficiently solve is a strict superset of the class of problems classical computers can

It isn't even clear whether the class of problems quantum computers can efficiently solve is a strict superset of the class of problems classical computers can efficiently solve, before you even consider whether it's clear that we can build quantum computers with any reasonable number of logical qbits: https://en.wikipedia.org/wiki/Quantum_supremacy https://en.wikipedia.org/wiki/Quantum_supremacy