Olympics Dolby Vision

Ch 1350 is USA4K Olympics coverage.  I get HDR on my XG1v4 DVRs, which don't support Dolby Vision.  The image is bright and colorful on both of my LG OLED TVs.

Comcast promoted Dolby Vision on USA4K using Xfinity Stream.  I've tried it on both a Roku Ultra LT and Fire Cube 3rd Generation.  I get Dolby Vision just fine, but the image is dimmer and colors are not as vibrant.  Brightness and colors are fine with Dolby Vision from other apps like Netflix on both those platforms. 

Anyone else using Stream for Olympics Dolby Vision and what do you see?  Thanks.