There are a few videos out there explaining our approach and how well (or not well) it worked and why. McToms un-involvement wasn't just due to the system, it is the player and he managed to be invisible in quite a few different ones. The system/approach itself made sense (extent might be debatable but it isn't 0) and it worked well for 20 minutes and decently for the rest, the issue was that Brighton found a way around our plan and capitalized while we seemingly didn't have an idea to adjust to their adjustments.
Agree to your mostly, just want to add that just because Amrabat may be deeper positioned than Casemiro, he doesn't necessarily has to play the defensive role. Think of Pirlo at Juve, he played behind Vidal and Pogba or Marchisio, he took the ball from the defenders and organized the buildup. He was the deepest midfielder, but he wasn't tasked with doing the dirty work. Systems can be made functional on a million different ways. That is a bit a dilemma right now - the sample set is too small and the injuries list too long to even try to grasp what ETHs plan A is. I agree though, that the midfielder we have aren't setting them up themselves in terms of "this is his best position". Adjustments will be needed. Probably a few pretty creative ones as well.