This is a constant frustration for loyal DJI customers, but there is a very good reason there ISN'T better forward compatability with DJI remote controllers: DJI keeps advancing and improving the transmission protocol between the RC and the drone, and older controllers usually don't have the right hardware to upgrade with a simple firmware update.
Lately DJI has, to the benefit of their customers, been addressing this. Standardization of the RC-N1 across the product offering, and more forward upgradable because of the more generalized SDR (Software Defined Radio) implementation.
This allowed using a mini 2 RC with a Mavic 3, A2S, M3P, etc, so one could buy drone-only and upgrade. The RC-N1 is upgradable from O2 to O3 with just a firmware update.