Each time I've looked into the react based static site generators, even late last year this seems not to be true, at least not easy, they always seem to bundle client side js for rehydration, turning that off seemed impossible and wasn't a priority seemingly for many generators because the site would work without js enabled, but for cases where I don't want my sites payload to include a huge bundle of needless js then I was out of luck.

This is a good point. I've been very impressed with how well Nuxt works for static builds: https://nuxtjs.org/blog/going-full-static.

I think for a startup with the liberty to choose a new tech stack, Nuxt.js is a great choice. It allows you to start with simple S3 bucket hosting, and move up to Vercel/Docker on ECS/etc. as you grow.

Hugo is a fantastic choice for blogs, but not for much else.