Who said "flat"? Only you my friend.
Even when Davies played at West Ham, Aurier was bombing on (unlike, obviously, Davies). Verts obviously stays home, and it is all a bit more of a (GG-phrase coming up) "wonky"...call it what you like, Aurier's defensive shape and levels of responsibility are appalling if we want to keep clean sheets/games tight. Mourinho obviously took one look at everything, realized our defense needs serious help and decided to try and score more than the other lot, gambling on Aurier's attacking "skills" outweighing his poor focus and gaffes defensively. The time has come to call an end to it, if only because we have a CB who simply has no legs anymore either, so really cannot be fudging around like this back there.
Imagine if we had a right back, or even wing back, who knew shape, who worked well with his immediate team-mate (in this case Moura, who I am afraid to say costs us too thanks to a sheer lack of awareness/switching off) and redid not have to always (and I mean, always) rely on Sissoko to drop in and cover. Perhaps -just perhaps- we could play more creative deep lying midfielders on a regular basis.
You keep banging on about Mourinho asking Aurier to play that way. I have no doubt he is. But do you think he asks him to trot back when left out of shape, to make mistakes, and to generally brainfart 30% of the time he is asked to do something defensive?
I understand you appear to like him, but please understand the counter-point even if you don't agree with it. It is not a hard point to gauge.