I'm not so sure about those assumptions. Using 1.0 with latest AGP will likely be recommended, but I assume that the AGP team is on a different release schedule and won't necessarily move to stable just because compose goes stable.
As far as using 1.0 with agp 4.2... there doesn't seem to be anything preventing that from not working anymore (see:
https://marcellogalhardo.dev/posts/2021/03/30/using-compose-beta-on-as-4-1/) it looks like all you'd lose is the tooling in the IDE.