Before rails there was LAMP. That's what Facebook used. Java servlets existed as well. And rented clouds existed before AWS as well. Despite the hype for them on pages like this, neither AWS nor Rails were really big disrupting inventions. The market for both existed before them, and will exist after they've fallen out of favour.
Where innovation happened is in the scaling domain. Terraform, kubernetes, etc, as well as in the SaaS tools you mentioned. But most of those things aren't needed for earliest stage startups. You don't need to be super scalable from day one. You can just run everything from one very powerful box for a while.
Of course this all depends on what your application is. If your product is a cloud based tool to post process movies, it will be a different setting from a CRUD app to plan events.
