Cloud run is developed by the same team that built AppEngine. They share the same technical leadership and a lot of the technical stacks, for example, billing and security (gVisor).
I dont think it's that simple to replace one service with another. It requires a lot of very sensitive dealing with external customers. And one cannot (easily) use the typical "Google deprecation" on a Cloud service offering, either.
So it's complicated. But your impression is not too far from the inclination.
I’d imagine google would at-least make both appEngine run on the same core primitives that cloud run uses. So while the public facing api is the same, the internals are replaced. At-least that’s how I’d approach it. Deprecate app-engine in that it will be infinitely supported until the last customer, but all new stuff is advocated to be used on cloud run.
One would assume transition from AppEngine to Cloud Run would be directed by establishing a pricing differential that incentivises moving off AppEngine.
I dont think it's that simple to replace one service with another. It requires a lot of very sensitive dealing with external customers. And one cannot (easily) use the typical "Google deprecation" on a Cloud service offering, either.
So it's complicated. But your impression is not too far from the inclination.