I'm pretty skeptical of the SMR thesis, but I think there are plenty of examples of modularization and miniaturization being economically advantageous.

For instance, I just the other day came across an article about how in the first wave of electrifying the textile industry, they replaced big centralized steam engines with big centralized motors. But then they realized that motors made it possible to mass produce small machines and put one at each station, and they turned out to be an advantage.

I think there are a number of specific reasons to be skeptical of SMRs, but I don't think the entire concept is per se flawed.