The argument is that small-scale nuclear reactors have been built for military and scientific applications so the tech is not especially novel.
What I think is unproven is whether SMRs can be built and run safely while being cost-effective to other forms of power.
I wouldn’t be surprised, for example, if it actually costs less to build and run one full-scale reactor than it does for multiple SMRs of the same output.
That doesn’t mean they won’t have a use.
And I personally have switched from bull to bear on that. I was rooting for NuScale but they're hitting the same thing as everyone else.
Meanwhile, battery storage has been on an insane cost reduction curve.
It is the same argument I make for Starship. Technically, yeah it should work. The economics of of going to Mars, not so sure about that.
But despite SpaceX's huge successes with Falcon, that doesn't prove they'll cross the finish line with Starship. Falcon and specifically the Merlin engine made just about every choice they could in favor of risk reduction rather than the best possible performance. It was a continuation of work that Tom Mueller did while at TRW.
With Starship they're in more uncharted territory, especially the re-entry concept, and the engine has been designed under the opposite philosophy of trying to push limits.