Sulked for 2+ years? He was poor at the start of Mourinho's first season but improved a bit by the end. In Mourinho's second season Martial was our best left attacker (comfortably better than Rashford even though it took far too long for Mourinho to acknowledge this) until he was stupidly dropped when we signed Sanchez who never got close to the level that Martial had been playing at. He barely got a chance there again until Mourinho was about to be fired in his third season, at which point Martial instantly came in and, along with Pogba, kept him in a job for a couple of extra months.
Martial was poor in 16/17, particular at the start of the season. There were a number of different things that happened at that time that could have caused it (which I mentioned above), or likely a combination of them all. I would hazard a guess that his personal life issues and change to a new position were likely the biggest contributors, but that's all it is - a guess. You are the one trying to claim it definitely was because his number was changed and hurt his business, using false evidence (sulking for 2+ years).
False evidence?
He lashed out in media over it before the season even started and played awful.
He is a professional Footballer not a clothing salesman.
If he chooses to cheat on his pregnant partner, that's on him and if he cannot separate personal and outside of football matters over his paid profession, than it IS all on him sulking, because i'm sure he isn't to blame for any of it.
Watch his attitude on the pitch and body language, it's 100% different and the only time, it's changed since then, was after lockdown last season, but this season sadly, he was poor and his body language changed again. (I believe again, to other off the pitch issues at home).
The guy is just the same sadly as Pogba and the team cannot afford to carry one, let alone 2 people, who are not mentally strong enough, to focus on there Job.