I don´t think you really understand what i mean. 🙂
There are two possible problems in your situation:
1. Your CPU usage is at 100% and you GPU usage is at 85-90% or even as low as 40% (I had that problem when BFV came out). In that case Your problems occure due to you GPU no being used to its full potential. The solution for this you can probably find in your settings as I said before. I had to change to DX11 and FFR on for my GPU to start working properly. This might be different in your case, so just try different combinations of these settings.
2. Your CPU as well as your GPU usage is really high (95% or higher). In this case there has to be a different problem, when you´re still getting lower FPS than you did with the RX card.
For this reason I´m asking what your GPU usage really is. 🙂