These quantum Monte Carlo simulations are only necessary because we don't have quantum simulators [1], so yes while a quantum computer would not necessarily solve the sign problem, it would make it irrelevant.

[1] https://en.wikipedia.org/wiki/Quantum_simulator

QMC computes multiple superimposed versions of classical MC at the same time, giving a polynomial speedup, not good enough for NP hard problems.

QMC cannot speed up simulation of a different quantum system - unless you're simulating a strict subset of your specific machine.

Quantum simulator is not a QMC system - it is designed to exhibit same behavior as a modelled system. That makes it somewhat useless for a system whose properties you do not understand. Any grid of fermions does not act like any other - if it did, BCS version would be accurate.

I don't think you understand what quantum monte carlo is or why it works. Nearly everything you've said is just plain incorrect.

Furthermore, I never said quantum simulation was QMC. I said that having quantum computers able to simulate many-body Hamiltonians would make QMC irrelevant, or at the very least would not suffer the same limitations that QMC suffers, specifically for strongly correlated fermion problems.

I suggest getting a stronger grasp on the literature before you go around making claims like this. Whether you know it or not, you're actively spreading misinformation and making the internet a worse place.