This setup is absolutely the ideal. Sadly it doesn’t often survive first contact with reality. Bob in sales will sign up for a tool that suddenly becomes load

This setup is absolutely the ideal. Sadly it doesn’t often survive first contact with reality. Bob in sales will sign up for a tool that suddenly becomes load bearing, and it doesn’t support SSO without a 10x increase in the monthly fee. A million dollar client needs you to integrate with one of their services which only supports a single shared API key. And so on. You also have to consider whether doing the heavy lifting required to get to this point is really the highest priority for your one man company which is yet to make a single penny and has no customers. What you describe is certainly much easier to implement early on when you’re not dealing with a ton of legacy services, but it will still probably take a few weeks of work to make it reliable for everything.