HEVC export 20x slower on 15b5 than Apple Compressor

I have a 16 minute video that DR 15b5 can render to ProRes HQ (422/10 bit) in about 4-5 minutes. Rendering to HEVC (H.265) takes about 2.5 hours. Rendering HEVC 10 bit on Apple Compressor takes less than 6 minutes, which is more than 20x faster than resolve.

Looking at my AMD Radeon Pro GPU History window, it's obvious that DR 15b5 is barely using the GPU at all.
Compressor doesn't throttle the GPU by any means, but it clearly is using it at about the 10%-15% mark all the way through the render.

FCP X COMPRESSOR : I also noted that Apple are firing HEVC compressor compute to the both threads of each CORE - and also run at a super high efficiency rate.

As both programs can run concurrently - decided to use R15b5 -> export at the highest quality possible (that takes the minimum export time to deliver in Resolve) and let FCP X to final compression.

AJ