"Compatibility mode", "emulates", and " not coded for RDNA 2", it literally can't get any clearer then that.
while Series X runs old games with full clocks, every compute unit and the full 12 teraflop of compute, it does so in compatibility mode - you aren't getting the considerable architectural performance boosts offered by the RDNA 2 architecture.
What are the considerable architectural performance boosts offered - VRS and Mesh shaders and SFS - what else ? I said that. These need to be programmed.
Fafalada also mentioend this, most architectural improvements are not turned off and on by game code, its api driven.
Features he is talking about VRS, Mesh shaders and SFS and things you need to program for or recompile.