Having a "stable" and "dev" cycle would be advantageous, yes. But probably the developer-resources required are not to be underestimated.
Also, Apple couldn't lock-out firmware-downgrades that easily anymore and I guess they'd likely introduce even more bugs trying to back-port fixes to iOS versions older than the current ones (due to sometimes big changes under the surface). I.E. if a bugfix requires a fix in a framework that didn't even exist in the previous version etc.pp.
Their internal bugzilla (or whatever they use - would be interesting to know what actually scales to their level) must be a horrible sight.
(For a glimpse of how that could look like, take a look at the issues in Open Source Gitlab:
https://gitlab.com/gitlab-org/gitlab/-/issues - but probably it's much, much "worse" for iOS).
I can live with not upgrading to the latest and greatest at release-date - but then, I also don't think I've got nation-state adversaries that require me to run the latest hardware and the latest software at any given time...