I don't think they knew what RDS is/was. We heavily rely on AWS but can move off with little work. You have to decide from the start if you don't care about possibly migrating off AWS or not.

We chose to keep that ability to migrate off. In hindsight it was a little more thought up front but little to no additional overhead now.

AWS provides a ton of open source compliant services. When you decide to use a proprietary one just build in the appropriate abstractions.