I think this issue is likely to be diminished as the performance difference's not been improving that much lately (X and XS having similar CPU performance) - we

I think this issue is likely to be diminished as the performance difference's not been improving that much lately (X and XS having similar CPU performance) - we have come to a point of smartphone evolution where yearly additions to a performance will not be the reason to upgrade -> therefore I don't expect new iOS versions slowing devices significantly.