You're outlining all the reasons why Cloud Run is the successor to App Engine.
App Engine was the very first PaaS, came out before Docker, and did things very uniquely in order to try to only allow scalable apps. App Engine standard has to explicitly create special environments for each of their runtimes, and that's slow and expensive. Services like Datastore and Memcache were tightly coupled.
Cloud Run fixes all that. It's just a Docker container that listens on the PORT env variable. Use whatever runtime you want. Run the same container locally, or on another cloud provider. The other services like Firestore or Memorystore (Redis) are truly optional and external.
Cloud Run is what lets you avoid single-vendor lock in, but still get from 0 scaling.
My understanding is that the 'flexible' version of App Engine runs on the same infrastructure as Cloud Run (and GKE for that matter). IMO running a regular node express app on Node Flexible App Engine isn't that different from running on Cloud Run, and I'm not really using any specific App Engine services (e.g. I don't use datastore, just a regular postgres DB on Cloud SQL). Lets me get up and running quickly with the knowledge I can easily containerize it if needed.
App Engine was the very first PaaS, came out before Docker, and did things very uniquely in order to try to only allow scalable apps. App Engine standard has to explicitly create special environments for each of their runtimes, and that's slow and expensive. Services like Datastore and Memcache were tightly coupled.
Cloud Run fixes all that. It's just a Docker container that listens on the PORT env variable. Use whatever runtime you want. Run the same container locally, or on another cloud provider. The other services like Firestore or Memorystore (Redis) are truly optional and external.
Cloud Run is what lets you avoid single-vendor lock in, but still get from 0 scaling.