I had the chance to have a call with Holly Borla this past WWDC and what follows is my understanding of things:
I don’t view approachable concurrency as training wheels. The vast majority of code is single-threaded, so Apple is now allowing one to more easily adopt Swift 6.
Even for software making use of networking, Apple’s APIs (e.g. URLSession) already allow you to use async/await. Work will be done on a background thread, and when returning, you can be on the main thread to update UI. No actors needed here at all.
In addition, there’s the default actor isolation setting. Holly had recommended that most projects should have approachable concurrency enabed along with setting the default actor isolation to MainActor.
This has worked well for my own projects as the amount of @MainActor throughout the code was almost eliminated.
With that said, there was an issue with the earier implementation of Swift 6.2 where one still needed to sprinkle in @MainActor (resolved with Pull Request #82383).
Though there’s still a remaining case involving Equatable which is either a bug, or a specific situation where @MainActor still needs to be specified. See: Insight needed for Equtable with Default MainActor Isolation