At any club where he has managed more than 2 seasons the 3rd season has been the worst. Might be a statistical quirk but might point to a downside of his managerial style.
What should happen for you and other Jose acolytes to admit that you might have been wrong about him? Would a season without top 4 and without a trophy be enough? Show your cards.
I would say its a short sample space.
Mourinho has had six tenures as manager of a top flight club with two of them (porto and inter) being only 2 season long. looking at the other four
1. Chelsea I - left a few weeks into 4th season. After winning the league 2x in his first two seasons and cup double in the 3rd, Mourinho had clashes with Avram grant who Mourinho objected to his appointment as DOF and who he accused of backseat managing the team - something further supported by Grant taking over as coach after Mourinho left. After Mourinho left, Chelsea subsequently went through 8 managers in 6 years, with the longest tenure being Ancelotti with 2 seasons.
2. Chelsea II - left mid-way in 3rd season. Again, after winning the league in his 2nd season Mourinho clashed with backroom staff over the failure to sign john stones. His successor in Conte lasted only 2 seasons, unsurprisingly over disagreement with backroom staff on transfers. Sarri is still early in his stint
Overall, Mourinho's two tenures are the longest of any manager under Abramovich (no other coach has made it into the 3rd season) and thus it can be said that the problem is more with Chelsea backroom than with Mourinho. In fac, Mourinho probably should be credited for lasting as long as he did with Abramovich.
3. Real Madrid - left after 3rd season. Mourinho was doing well at Madrid, wining the league in his second season, but ran into locker room problems, particularly when he decided to bench an aging Casillas ( a decision later borne to be correct by subsequent managers doing sameand Casillas being eventually sold). The locker room problem is a cancer that has always plagued madrid, with players with close relationship with Perez undermining coaches (e.g. Toshack was sacked for asking Zidane to simplify his game). Maybe Mourinho could have managed things better, but he has his own character flaws and has never been one to shy away from conflict. Still the problem at Madrid , starts and ends with perez and Mourinho lasted longer than most, with lopetuigi being the latest scapegoat of Perez's mismanaging the squad. That there are rumors of him managing Madrid again shows that his relationship with Perez is still good.
4. United - 3rd season exit? The first two season went reasonable well imo and team seemed to be moving in the right direction. the failure of the board to fulfill his request for a CB (which i dont think is enough to competefor the PL against Citeh) makes it impossible to know if the progression would have continued. This brings up what I think is one of the risks with Mourinho - his dissatisfaction with things off the pitch is often coupled with poor performances on the pitch. Dont know if it is deliberate on his part but would be surprised if it is not. Unfortunately, while this may make a point to the board, it often loses him support with the fans. Also, managers (like ancelotti) that often take it quietly, seem to get more abused by the board (while Mourinho either gets his way or get fired with a nice pay off).
I think anyone hiring Mourinho should be clear on what they are getting and if they are not willing to provide an environment that would maximize his output, should save themselves the drama that would likely follow when differences arise.