Plus, you can generally take the the dynamic generators and dial them down to a purely static build for sites that genuinely aren't using client-side features, but you can't go in the opposite direction.
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.
The React SSGs are not very good at this, but as mentioned in my reply to the parent comment, Nuxt.js (based on Vue), is a great option. See https://nuxtjs.org/blog/going-full-static.
I've done the "turning off javascript" thing with next. It involved a minor override in _document.js to avoid generating the script tags. Not officially supported, but not hard either.
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.
