RoR wasn't picked up by e-commerce at this scale. Most of the craziness comes from attempting to squeeze out every last inch of performance so that the prospective client won't go "neeeih" and shop somewhere else.

A RoR app will just sit comfortably wherever you deploy it, slowly doing its job like a good, reliable tractor.

A typical Next.js app is smeared all across its origin, some geographically convenient Edge and the frontend. It's a very different use case.

what do you mean? Shopify is the largest eCommerce platform and runs rails.