Yeah but stats support that argument! If we were judging him by stats he'd have had a good season but it depends on what stats you value, it depends on what you mean by 'consistent', Chelsea last season were consistently clinical and that's why they were champions despite not showing consistency in their performance, if Angel di Maria has been consistently productive even if his performance hasn't been consistent then surely he could still be considered world class?
I know you said 'world class' is a nasty expression, I don't know exactly what people mean by it but I'd say Angel di Maria is one of the very best wingers in the world.
The problem is linked with our style of play, every player is an important cog in the team machinery, we can't allow a player to fail on the basics on a regular basis, Di Maria lacks consistency with the easy things, he can destroy your team play very easily but he will also create opportunities very regularly, if we are clinical and transform most of the chances created by Di Maria and/or if we managed to be a team that retake possession very easily then we can offset Di Maria's flaws and benefit from his huge qualities.
For the clinical part, I think that Depay and Rooney playing with him will fix that problem and for the retaking of the ball, Schneiderlin, if we sign him, will help a lot.
So I'm not for Di Maria's selling but I can see why a coach would choose to do without him, it's a bit like Mata with Mourinho sometimes quality players don't fit in the schemes.