Looking at Supabase, I think it would be a good choice for most startups[0] and it will scale as the business does, but it removes most of the overhead of getting started. It has Auth, A database, Lambda Support, CDN and File Storage. Baked in are REST APIs and GraphQL APIs out of the box.
Its reasonably well priced and there's little friction on setting up and far, far less to worry about hosting wise. No need to setup a box and maintain updates etc, and it can scale if the business really does scale.
I don't think all cloud propositions are the same. AWS, GCP (maybe sans Firebase?) and Azure definitely have their place but I don't think they're great for the average startup.
[0]: Even medium sized and enterprise businesses could leverage it. Its all powered by Postgres at the end of the day