For me it's irrelevant to say what other players have/ haven't done as a bearing on what happened to Marcus as if there is one case then it suggests it's possible, for which there will be one. I agree the club could have done more and done better 100%, perhaps it was the initial wording I took issue with, we promoted him paid him 300k a week and gave him superstar status and typically he pays that back with lack of work, going out clubbing and appearing quite unprofessional at points which is why I think he has failed the club.
We definitely could have done more for him as we also seem to bow to his notoriety and seemingly can't drop him or criticise him due to the size of his brand and the power of the PR around him, I'm not even referring to how bad he has been but I just want to see more from the person. Let me float a scenario: He has the same season this year in terms of output but he is the consumate professional, regularly states he is working harder and the manager attests he is in earlier, stays later and on the field we see a man giving everything with his defensive work, willingness to pass (Not always the cut in shoot) and contesting for every ball: That's a player I am fully behind and will support so for me I wouldn't look at it as he didn't score enough, he's failed us, I look at it as his effort/ professionalism and desire can be questioned very easily with the optics test and that's a foundational thing to make sure you have, it should be a pre-requisite, like us paying his salary or giving him somewhere to train.
To simplify it as I have a tendancy to waffle:
Player requirements
Level 1: Give everything and be professional but awful output
Level 2: Not professional or giving everything but have a great output
Level 3: Give everything, be professional, great output
Club requirements
Level 1: Pay Salary
Level 2: Give Coaching, tactics, ample opportunity
Level 3: Top quality environment, top quality coaches and superb tactical advise with discipline in the hard times
My feeling is we as a club are giving him level 1 & 2, he isn't giving level 1 so I had the wording of "We failed him", we could have done better for him but I think he's failed us..