If you plan to scale to that extent, then why do you not have the money to hire the people who can use AWS? At least part time or as temporary consultants.
This:
> The point where you get sticker shock from AWS is often significantly lower than the point where you have enough money to hire in either of those roles
makes me doubt this:
> AWS is obviously the infrastructure of choice if you plan to scale.
I'm wondering what the point of all of this is.
If you can afford the large fixed cost of vertical integration, it's always cheaper to do things yourself, so the sweet spot for using providers like AWS is scaling down, not up. A managed DB lets you hire a fraction of a sysadmin or devops person from AWS.
The moment you end up paying enough to AWS to hire a sysadmin, you basically are getting an antagonistic sysadmin from AWS, whose primary goal is to make as much money off you as possible. The incentives are not aligned.