Why people keep repeating that? You mean that if somebody creates a machine that can simulate chemistry and materials science in polynomial time, nobody would use it? That's crazy.
I have no expertise in QC/chemistry so I can't make a judgement other than to say it doesn't seem universally agreed that QC will be a silver bullet here.
That's quite similar to claiming that quantum computers won't change anything for RSA cryptography, because we never had any proof that integer factorization can't be done in polynomial time on a classical computer.
The paper also shows that the proposed QC strategy for calculating energy levels - where you start with a guess and then optimise - may not lead to exponential speedup on a large class of important chemicals, because just coming up with an appropriate initial guess has no polynomial time algorithm at present. So it's not clear for what class of chemicals this would even theoretically become a tractable calculation.
