Depends what games you focus on. When his head is screwed on (Argentina) or certain Spurs games (Europa League knock out games where he ended up player of the tournement) then yes he is world class. He is one of the best in the world on a going day! That is fact.
But I agree with what your saying. His consistency has been shocking for us. Was brutal at the start of last season and he tends to miss close to 50% of games a season. I still think you have to try and keep these players and get them onside! He just needs the right environment.
In his defence, he is way too good for us. Must drive him mad playing to get top 4 when really he should be competing for the PL and CL but the players around him are nowhere near his level. He shouldn't let all that effect his attitude and performances so thats where he goes wrong, but when he smelt that Europa League trophy he turned into Maldini for those last few games and in the final!