My Apple devices always seem to slow down over the years
You have several options to fight against the slackening of your devices (or the perception of it):


don't install apps (especially apps bloating over time because of feature updates)
don't use faster and newer devices of the same kind (or better: the older your own devices get, ask friends or colleagues to lend to you their much older and slower devices more frequently and use them and you will happily return to your own "faster" device)
get old faster than your devices (or reduce the perception of speediness or responsiveness artificially)
take Zen lessons