While this is mostly true. There is also a lot of truth in the argument that nuclear reactors are somewhat dangerous. I often find that the danger is exaggerated, but it does still exist. For instance, how much less stressful would the Russian attack on Zaporizhzhia have been if the reactor vessel was a mile underneath the area instead of on the surface. How much less of an issue would Fukushima have had if the spent fuel pool had been a mile under sea level?

If running reactors under the surface isn't significantly more expensive than surface containment then I think it's a wonderful idea.