I just checked, Google and Amazon still work flawlessly without JS. And many other "useful products" too.
The question is, if a startup can't make a site that works without JS, are they actually focused on the product? Assuming it's not a webapp, of course.
You're making two completely different versions of your web product: one with a rich, modern experience using JavaScript and the other using vanilla get/post.
I've built several SaaS products and I can't imagine building a complicated product that supports both a JS and no JS version with a small, startup team.
The question is, if a startup can't make a site that works without JS, are they actually focused on the product? Assuming it's not a webapp, of course.