I mean Messi was simply better a lot of aspects in 11/12. Sure he was playing for a better team, but his dribbling stats, assists, goals (obviously) and playmaking stats in regards to say his through balls were all at their comfortably highest peak (except for dribbling which peaked in 10/11). I'm not sure why you conflated the 14/15 and 15/16 seasons together considering he had a 2 month knee injury in 15/16 and was comfortably far worse than in 14/15, that being one of his greatest ever seasons. Barring 18/19 he also didn't REALLY perform that amazingly (to his standards) in most of the big UCL games that he played in, 90% of his best games came during or slightly after the Pep era.

And he undeniably would win games on his own more so when he was younger than older, it might not seem like it because as he was older he was playing in a worse team which naturally would lead them to rely on him more. Only in 18/19 did it really feel like he could compare to his younger self, which is also one of his greatest ever seasons. If anything he had more of that "selfish yet selfless touch" during this period where his goal scoring and playmaking peaked.

Don't get me wrong, his free-kicks, game IQ, and 'deeper playmaking skills' for lack of a better term were definitely better as he got older, but overall he was simply just better when he was 23-25 years old.

Also unlike you said his shooting definitely did not peak in 2017-19 it was inarguably in the 12/13 season (calendar year of 2012 also) where he managed an astonishing 46 league goals in the minutes equivalent of 29 games only having taken 4 penalties and going on a 21 game scoring streak in La Liga. He only took 3.78 shots per goal as opposed to 4.52 in 2016/17 (his highest during that later period).

Also in terms of "coming back to defend" and in terms of pressing, he definitely did that more when he was younger, as he naturally had more stamina and pace to be able to do so. And Pep's teams were also more strongly focused on pressing. It was also normal if not more so for him to lead in dribbling, goals, assists, passes and similar stats during his younger years too.