You are not alone. There are many people posting these issues. And there is no real answer just yet. The card is well optimized to work in Superposition, 3DMark, etc. You should be able to run them at stock settings and get a good score. However, in certain games is where the problems start.
What is happening is the 5700 XT aggressively downclocks the moment it detects no activity (more or less). Not only will it drop the clock but also reduce GPU usage. It's a forced behavior. To those who either don't experience this or haven't looked into it will assume you have a CPU bottleneck (which is kinda hard to make in your case). For some as soon as they see low gpu usage they automatically assume CPU Bottleneck.
This is actually the behavior of the GPU and the drivers. Right now it is highly recommended to disable any hardware acceleration in your web browser which is an absolute sign that the boosting nature of Navi is fubar'd in some way. In games like BFV you have to enable future frame rendering. In other games do not set any frame rate caps as that too will fubar the boost feature in Navi.
Do not use Chill (that too is fubar'd). Open up Regedit and do a search for ChillEnabled it will show you a "invalid value". That hasn't been fixed for months now. To fix it yourself you will need to delete it and rename it ChillEnabled (Use Qword). And for now just leave it at 0 (a lot of debate back and forth if 0 is enable/disabled).
Since you already did a clean 1903 install you did what you should do as the drivers (so I'm told) are 1903 "friendly".
You want to pickup a program called Intelligent Standby List Cleaner.
Use it. It will get rid of some of the stutters. It not only removes standby list which does cause stutter in game but also let you set a timer resolution to 1.00 or 0.50. It's kinda tricky though. You have to stop it click on the value with your mouse pointer hit enter then start it. Current Time Resolution should drop to the value you set.
https://www.wagnardsoft.com/content/intelligent-standby-list-cleaner-v1000-released
Set your bios PCIe3. Mainly for those that have PCIe4
Review and research Window Defender's cheeky Exploit Protection which is found in 1903. I don't recall which one you need to disable.
Other then that. Wait for AMD to release drivers to address it. However, it would be nice if AMD 1st acknowledge the issue.
Links:
https://www.reddit.com/r/AMDHelp/comments/dgadb9/has_anyone_fixed_this_5700_xt_crazy_clock/
https://www.reddit.com/r/AMDHelp/comments/dg9c9d/my_rx_5700_xt_performance_help/
https://www.reddit.com/r/AMDHelp/comments/dgengm/low_fps_even_when_gpu_isnt_maxed_out/
https://www.reddit.com/r/Amd/comments/dfbn2b/temp_solution_for_rx_5700_xt_bfv_low_fps_low_gpu/
https://www.reddit.com/r/AMDHelp/comments/dghx3z/5700xt_performance_question/
https://forums.overclockers.co.uk/posts/33077063
https://www.reddit.com/r/Amd/comments/dfbn2b/temp_solution_for_rx_5700_xt_bfv_low_fps_low_gpu/
Edit 1:
As to 19.10.1 I am able to finally play BFv. But I had to use a few tricks to get it to work in combination to 19.10.1 (not ideal I should be able to plug/play). Other games do appear to keep it's boost better. But still observing.
Edit 2:
I also suggest that you take a look
at this thread.
Then follow the instructions on this pic if you have a freesync monitor. You are making freesync 1st.