Not all TMTOs are linear...
Some PoWs need q^2 more time to use q times less memory,
which you cannot overcome with a quadratic quantum speedup.
I agree that it's possible to create an algorithm that will be too hard for available quantum computers, it can even be modified each month to keep new QCs out of business all the time. The question is: Will
ordinary users be able to run such algorithm? If not, then we'll get Animal Farm scenario becoming the reality - We'll trade one master for another.