Yea, that's fairly normal for Gylt.Oh, I see. Thanks!
I gave Gylt a go and it seems nice, but the compression is a complete dealbreaker unfortunately.
Is this normal?
(I'm on a 1000Mbit connection with 2ms ping to the Google center, so connection shouldn't be an issue)
It uses a lot of blacks and heavy dark gradients, which any video encoder is going to have problems with. You will see something similar if you play Thumper and look at the background.
Most games don't have quite the same problem as those 2 just due to their graphical design choices, and to be fair, it never impacts how the games play, its just one of those things that'll happen when you use a video encoder. Its a trade-off between speed and accuracy. If Google went for better accuracy, each frame would take longer to encode and add in more lag.
Give Spitlings a try. That has huge blocks of colour but seems to look perfect on my setup. I'm using a Chromecast Ultra though (but only at 1080p).