I'm also very sensitive to UI lag, but flagship phones are more a cause than a solution.
If you're on Android, enable developer options and disable animations. Not only is your phone now many orders of magnitude more useable because it's responsive to your actions instead of being in store demo mode with UIs built for videos in marketing banners, you can also use an old phone very comfortably.
I use a five year old mid tier phone quite comfortably. There is the occasional app that stutters because it bakes in its own pointless animations or NIH smooth scrolling, but this is easily solved by not using broken software.
If you're on Android, enable developer options and disable animations. Not only is your phone now many orders of magnitude more useable because it's responsive to your actions instead of being in store demo mode with UIs built for videos in marketing banners, you can also use an old phone very comfortably.
I use a five year old mid tier phone quite comfortably. There is the occasional app that stutters because it bakes in its own pointless animations or NIH smooth scrolling, but this is easily solved by not using broken software.