I've claimed that it's the only thing we've objectively learnt - perhaps I wasn't clear. There is no debating that some players are definitely better than they were before Mourinho left, and there's no debating that others have been equally abject since. The other points I've made are all arguable, and I might be backtracking on my opinions on them later on. Ironically, I didn't expect a Spanish Inquisition on that front.
This is one of those times where stats do not tell you the whole story. One goal conceded is a metric which needs to be taken with a pinch of salt.
Off the top of my head, here are defensive errors we've made:
Leicester: We were an Evans and a Maguire header away from conceding - both seemed straightforward. Bailly also made some bizarre decisions multiple times in that game, and Ashley Young played an entire team onside from that freekick where Vardy's overhead kick went straight to De Gea.
Newcastle: Rondon had a sitter early on which he dithered over before Jones tackled from behind. Atsu had multiple chances where he could have been through on goal and made the wrong decision. Our set pieces looked calamitous with Jones messing up big time.
Tottenham: Watch the highlights, and you'll realize how it was all De Gea. We were found out again and again - near post, far post, set pieces, open play - time and time again De Gea saved us. A good defence should not rely so much on the keeper, and our full backs had no idea where our center backs were. Lindelof perhaps the only other defender who did okay, everyone else was caught out.
We were lucky to not have conceded more. Also, I'm curious why you didn't include the home games, where Huddersfield, Bournemouth, Brighton and Burnley have all scored against us.
I agree with you on the bolded part, and Ole deserves credit for that - to keep the threat of counter attacks lingering in the mind of every opposition player charging forward to help their attack. I also agree that Ole is employing far less man marking, and that our full backs push higher up with exceptions here and there. But apart from Lindelof, I cannot see how any of our defenders have improved under him. Ole's defensive organization is yet to be properly tested, in my opinion.
That said, I'd be more than glad to eat humble pie over that assessment a month and half from now.