I checked some of this last night for you. Fubo no longer has Turner networks, so I could not compare CNN, but I did check out both MSNBC and Fox News (Fubo App vs Channels App) which have scrolling and fixed text. I checked out AMC and FX as you suggested too, but those were both showing movies and I think it's easier to spot issues with text or sharp lines on screen. I judged both streams for AMC and FX to be comparable.
In general, I felt that Channels (using TVE) and the Fubo app (on an Nvidia Shield) were pretty comparable. Fubo was much better than the Hulu app I used before. If I had to pick a winner, I would actually say that the Channels TVE feeds were just slightly better, but it could also be the timing of my back and forth testing. Both fixed and scrolling text were easy to read.
I uploaded photos that I took below. In these, the NBC Peacock logo is clearer in the TVE stream on Channels. This could also be just timing as the quality of various streams can fluctuate.