I agree with everything you'd said, but, to be fair, we're talking about different things. My claim was not about the complexity of problems, but the scaling of hardware -- which, as far as I know, scales sublinearly. This means that doubling the size of your computing cluster will allow you to solve the same exact problem less than twice as fast; and that eventually you'll hit the point of diminishing returns where adding more machines simply isn't worth it.

You're saying, on the other hand, that doubling your processing power will not necessarily allow you to solve problems that are twice as interesting; in most cases, it will only allow you to add one more city to the traveling salesman's itinerary (metaphorically speaking).