One way to test this problem is to compare the 5700 card with an RX580 series card. (or some RX5XX or RX4XX card series)
The RX580 card has a constant core clock during gaming. It only throttled once you hit temp limits or power limits. Unlike the 5700xt which is constantly switching the core clocks even when you are under temp limits and power limits.
Somebody could compare the gpu usage under both cards in the same scenarios. So run the same game in the same scene under a scenario in which you know the 5700 throttles the core. Take note of the gpu usage.
Then run the same scene using the RX580 card. The core clock will not throttle, but the gpu usage may dip down in the same manner as the 5700 card.
This will give us a more understanding on whether the problem is the boosting in 5700 card, or if the problem is overall with amd drivers.
I wish I had one though.
But I've read those with 480 and 580 not have the fluctuating gpu usage. Although they were not as detailed.
The overlay works, but the FPS counter in the Overlay is missing. And it's random.
I can repeat this. Use the OSD hotkey at desktop. OSD will show up (at desktop) without FPS counter. This is what I see in games at times (no FPS counter).
I can't say if this will work on R7.
I know, that happens to me often when I'm in borderless mode. Going into exclusive full screen always brings back the FPS counter for me.