I think the best example is in iOS. On old iOS versions, the keyboard responsiveness took precedence over everything, no matter what. If you touched the keyboard, it would respond with an animation indicating what you are doing. The app itself may be frozen, but the self contained keyboard process would continue on, letting you know the app you are using is a buggy mess.

Now in iOS 26, you can just be typing in Notes or just the safari address bar for example, and the keyboard will randomly lag behind and freeze, likely because it is waiting on some autocomplete task to run on the keyboard process itself. And this is on top of the line, modern hardware.

A lot of the fundamentals that were focused on in the past to ensure responsiveness to user input was never lost, became lost. And lost for no real good reason, other than lazy development practices, unnecessary abstraction layers, and other modern developer conveniences.