Ideas
i doubt this issue is related to new tech. it's more like how devs code and make videogames. didn't noticed any similar issues in other games (new and old), and, for example, new AC Rally runs and looks perfect on UE. coding skill issue
Could be a mix of both, as the issue atm seems exclusive to rdna4 in this game, while older rdna cards are fine (as rdna2 IME).
In the past, at EA WRC release, there was also the situation of NV Pascal cards having issues due to badly set shaders that somehow, other newer cards could eat up without glitching, masking an underlying code issue. It was fixed, but only after an unofficial patch was created by a private user to alert of the issue, and finally allow 1080ti users to run it. But now without support, and EA AC on top of it, chances are it'll never be corrected.