I wish I could verify but don't have this tablet, your welcome!Yeah, thanks for the replies. Clearly, something was either wrong with the tablet or what I was doing. Given that all other video sources looked great and others haven't encountered this, I'm inclined to think the latter ...
I was checking out a 7 Plus and looking at Prime Video and Netflix on both, the image was quite dark even with brightness all the way up on both the tablet and the apps. Is this a quirk of the tablet?