Android isn't a fair comparison, since Apple is a single-manufacturer monoculture.
Samsung-to-samsung: I can give anecdata only but moving to a new samsung phone was completely effortless. The only things that broke, broke because there was a newer android OS version on the target (not much of that). This would of course break (and maybe worse) on iPhone -> newer iPhone.
Samsung-to-samsung: I can give anecdata only but moving to a new samsung phone was completely effortless. The only things that broke, broke because there was a newer android OS version on the target (not much of that). This would of course break (and maybe worse) on iPhone -> newer iPhone.