I'm not entirely sure that what you listed is the reason SpaceX has been making such progress; NASA seems perfectly willing and capable of making cutting edge e

I'm not entirely sure that what you listed is the reason SpaceX has been making such progress; NASA seems perfectly willing and capable of making cutting edge engines (or rather, their contractors do). Whether or not their organization has the risk-taking and agility to change approaches like SpaceX does, that's another matter. However, I don't think in rocketry that "throwing propellant at the problem" is ever a solution, as propellant has weight. Efficiency is indeed incredibly important, because adding more fuel means having to lift more weight, which means you need a bigger engine, which needs more fuel to run, etc in a vicious cycle. One of the solutions of course, is to burn more of it at once (ie. multiple engines), but there's limits to what's feasible. (speed/atmospheric considerations.) In other words, it's not a linear matter of throwing more propellant. Costs can go up, quick. Coming around to the issue at hand, I can absolutely see having a high minimum threshold for a fusion power plant, where the plant needs to be large enough to generate a sizable return (excess power) for it's initial outlay, but also be able to make the maximum return (high consumption) of that power generated. You can build a massive plant in the midwest, but if the demands on it are quite low, then the economics of it doesn't work out. That means that the economically feasible scenarios for a fusion plant at this time are probably quite limited. I'm sure that will improve greatly over time. But it seems to be that the author's point is that right now, even assuming the technological issues are solved, it is probably isn't as cost-effective as some make it out to be.