Just playing devils advocate here, but I would say that Barkley, Stones, Deulofeu, Lukaku and Besic would have progressed whoever was the manager. They are extremely talented players who were always highly thought of and are now 22/23 rather than teenagers, so their progression is natural. I would argue that Deulofeu's progress has actually been a little slower than you would hope, particularly in terms of decision making and fitness.
I would also say McCarthy and Coleman are no better than they were 3 years ago. Coleman was already first choice right back despite what some revisionists will tell you, and i vividly remember having the conversation with mates at the time where we all felt we would rather Baines left for United than Coleman.
Lennon has definitely improved, to a player i never thought he would be. Mori has got better but again that may just be down to getting used to the league, same with Robles and Oviedo.
It's a shame that he hasn't got more out of Gibson, McGeady, Mirallas etc, and despite his good work with young players we've bought I do think it's a slight worry that not a single player has been promoted from our youth set up in 3 seasons.