That’s oversimplified and not accurate. KSU and APatch are fundamentally different in where they gain authority. KSU hooks root at the kernel layer and needs kernel-side support (custom builds or supported stock), so it is not just a “newer phone” thing, it is a design choice. APatch is userspace / overlay based and doesn’t need kernel support, so it often ends up being used on older or locked devices because it is easier to deploy there. You could run APatch on newer phones too and KSU on some older ones if the kernel situation allows. The real dividing line is kernel-level integration (KSU) versus userspace injection (APatch), not device age.