This is only partially true, France for example has standardized its reactors in the past, with a lot of success, and is planning to do it again for the new projects which are planned in the 2030s. Now it was done in the past with little care for local populations and so on, so we’ll see how it goes. What is true though is that standardization also makes sense when there is a repetitive market foreseen. New nuclear project tend to be announced in small numbers, due to the difficulty of investing so much capital at a time, which makes standardization difficult. Smaller reactors may help, but I remain sceptical with the tech.

Though efficiency is not really a relevant metric when the source energy is free. It has indirect impact such as the necessary area but efficiency is not a good indicator for solar overall. But yay science!