So at Milan the team regressed due to him and at Juve the team progressed/succeeded despite of him and due to Marotta? Milan had not won the league since 2004 when Allegri won it with them in 2011. Now, they have not won it since 2011. While they did have an expensive team they certainly did not have a Marotta at the time. In fact, you could argue being the coach at Milan in 2011 was just as difficult as being the coach of Man Utd in 2020. Probably even harder.
However, I do agree that Marotta did a great job with Juventus. Marotta knows his football. He also hired Allegri and decided to stick with him for a reason. Tactically, he is probably the best coach out there. He is very highly rated in Italy and with good reason in my opinion.
He inherited the best squad in Serie A when he joined Milan and below are quotes from the below link which supports that argument. I also never said he was solely responsible for the debacle at Milan but he played a large part in their malaise which is demonstrated below.
"In his first season Allegri had the best squad in Italy and was able to deliver a Scudetto. That team was star studded, and featured the likes of Zlatan Ibrahimovic, Thiago Silva, Alessandro Nesta,
Clarence Seedorf and an inspired Robinho. That squad, coupled with an extremely weak Serie A meant a Scudetto wasn't a pleasant surprise; it was expected, and Allegri was able to live up to expectations in his debut season"
His tactics? Quotes below by people who followed Milan.
"In his second season Allegri once again had the best squad in Serie A. This time, however, Milan choked during the run-in and coughed up the Scudetto in the final weeks to a
Juventus squad with much less quality. That famous
Sulley Muntari phantom goal certainly played a part in the epic collapse that cost Milan a Scudetto, but at the end of the day, it should have never been in doubt. With that squad and a weak Serie A, Allegri should have delivered a Scudetto. On too many nights it appeared that Milan didn't have a game plan. Their game plan was "give it to Zlatan and let him make magic." As Ibrahimovic went, so did Milan, and when he didn't have "it" on a given night, Allegri looked like he didn't have a plan B".
Just some of his crazy tactical decisions and bad decisions in general below at Milan.
"Allegri also made some crazy player usage decisions, like playing Urby Emanuelson, capped by the Dutch national team at left back, as a trequartista, or playing box-to-box midfielder Kevin-Prince Boateng on the wing, or converting mediocre midfielder Kevin Constant into a shambolic left back. The list goes on and on".
https://acmilan.theoffside.com/platform/amp/2015/11/21/9753256/looking-back-allegri-at-milan
I'm glad you somewhat agree with me about the superlative work Beppe Marotta did at Juve which for me was the main reason for their dominancy. I'd also credit Antonio Conte who was the coach at the time who helped put the wheels in motion.