Other teams have players off the boil, but this is ONE year for them, this is EVERY year for us. Mourinho is a bad manager who IMHO basically criticises and shouts to motivate players, in the short term they work harder, in the long term they lose motivation, aren't training well and become too intimidated by a shouting manager to even try anything. That team looked seized up from fear of what manager would say about a loose pass, with that criticism and black cloud removed they are one of the most in form teams in the league with the best players playing at their best.
Utd are in a rebuilding phase, have half the team out injured in any given week on top of that and new managers and new players to deal with. It's neither a settled squad nor a finished rebuild. Liverpool are under new management, rebuilding and need to do it again after buying mostly the wrong players. City have lost away form and have a semi crock yet brilliant striker and CB. An ageing central mid who WILL be replaced and years of not good enough buys filling out the team.
Arsenal are the only team with a manager who has been in charge for what, more than 3 years let alone a decade. None of these managers had control of ALL decisions in the past decade. None of the other managers chose EVERY SINGLE PLAYER, had complete control of the youth setups, the buying, the budgets, re-signing bad players, buying most of the bad players.
Wenger is in the same situation as exactly not a single other manager in the league, nor in the german or Spanish leagues. He is solely responsible for how the squad is, he's not taking over another managers mistakes, every mistake is his own. He has also purposefully ignored the fans, pundits, everyone who has pointed out the biggest problems. Every single other person in europe saw not buying another DM to be a major major problem, Wenger thought it was fine.
Wenger broke the bank to give Walcott even more money a week to be utterly worthless.