Earlier quoted context omitted.
I think this is less a "macOS lacks the feature to prevent focus stealing" and more they never even imagined the scenario where it takes time for the app to open. Instead of even considering that a user may add inputs while waiting for launch, potentially signaling that they are no longer requesting focus from the program they clicked on, they simply designed for the optimistic case where there never IS time for the…
As always, Apple has designed for the happy flow, and nothing else. Mac apps have never opened instantly, this is nothing new.
I can't believe in all these years they haven't implemented a dual setup where they connect the wifi and do some kind of test connection or request to confirm it's a stable signal before entirely switching away from cellular data.