I'm not from Laminar Research, just a fellow simmer in the UK :-)
On face value, your PC spec more than meets the recommended hardware requirements, although as you have highlighted, the AMD CPU and GPU is generally accepted to be less superior than the Intel CPU and NVIDIA GPU. Having said that, the former is somewhat cheaper than the latter, so it's rather a matter of how much you wish to pay?
To begin with, you may wish to run a little software program that can be downloaded free from https://cpu.userbenchmark.com/,
which will 'stress test your PC to see if there are any bottlenecks of concern?
Also, it may be worth looking at a YouTube video on X-Plane 11 settings, which was prepared by the well known simmer Q8Pilot. This video cam be found here:- https://www.bing.com/videos/search?q=q8pilot+x-plane+11+settings&&view=detail&mid=F0C0EB12F868099DCE34F0C0EB12F868099DCE34&&FORM=VRDGAR
A frame rate of 60fps for default aircraft is very good indeed, but why it should suddenly drop to 20fps for the FF A320, I can't really say? Yes the FF A320 is more complex and a study level aircraft, but the main issue is more to do with your PC's ability to handle graphics.
Other simmers on the X-Plane Q&A forum may be able to help further, but I trust this is of some assistance for now?