This feels like an Apple problem - their iOS variants being unified is a reasonable expectation from consumers and, additionally, the fact that they EoL devices so aggressively means that unless you're a cutting edge Apple follower a lot of their tech simply doesn't work together.

If Apple wants to sit there and say "Welp, buy the latest iPhone" they're free to do that - but the fact that there is user confusion is completely on them for making their products so inter-incompatible.