One thing that keeps coming back to my mind is Goldenboy and Mr X keep casually talking when something big happens off screen (Dva/Pulse bomb kills, Zen right click first pick etc). Now spectating can be tough sometimes for casters in Overwatch, but keeping track of the killfeed should be paramount to casters.
Other thing kind of related to this is they missed something like 2 reflected gravs (not sure about the number) the past 2 or 3 weeks of play. Those are huge moments cause they don't happen very often.
Mixing names/teams up happened way more than it should have, and hasn't been corrected by either party, so someone who isn't necessarily following the scene will get confused very easily by this.
Last point, which is critical and is what Monte, ZP, Hex and Uber do very well, is talk strategy during off fight screen time. EMP for team A, Zen will have to use his trance before it hits. Or trance for team A, Ana needs to position herself to nade it. These are just examples of what to expand on when nothing big is happening on screen.
Jokes and small talk are fine by me as long as they don't keep them going for a long time, which they do more often than not. And I feel like their deep understanding of the game is not there yet, and they struggle to fill down time with strategic talk.
Gb and X on first week were absolutely awful, which is understandable given it was their first game casted in a year or so. Huge improvement from second week onwards, went smoother and was more natural, but still not at the level expected. I'm sure with time and more work put in it, they'll keep improving.
I also find Mr X to be very monotonous, which throws me off a lot tbh, but that's just me.