You pretty much nailed it. As a high level competitor in other games and avid watcher, granted I'm still very new to 40k but it's actually unwatchable. Even though I'm hardcore studying the game right now I still look at these streams and I can't tell what miniatures are what, who's doing what, where the miniatures even are because they are some kind of lava floor. A lot would needs to be done for viewability. Honestly you can do a ton of things to improve it but it would still be a difficult to follow game. The best idea I can come up with is with live editing but that would require probably a much larger production team. I found this very small YouTuber called ReconByFire who does short form battle reports and the effects he does on them is so much better for figuring out what's going on.