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 user to give these inputs before their intention of opening the program is completed. Not saying it's any less bad from a user's perspective, but I think there's a difference in mindset here.