I think it's a bit odd to suggest that one of the most decorated players in English football doesn't understand about positional discipline while his many 20 year old team mates do. It's one thing to criticize his physical or technical abilities, but quite another to question his understanding of the game, because one doesn't lose that with age.
I have watched the Watford game again to try to find out what is it that you are talking about regarding his lack of positional discipline. Cmiiw, my best guess is that you think he should've stayed in the left wing as the left forward in a standard 4-3-3 in that game.
If you think that he has abandoned his supposed position on the left wing in that game, then I have to disagree. I think it's pretty obvious that he spent the entire first half in the center forward area, with Niasse playing effectively as a right forward as you bombarded the left side of Watford's defence throughout the first half.
I seems impossible for me that he would last 10 minutes being constantly out of position without Unsworth barking frantically at him, if that was not the plan for the game, or if he made the team to lose the intended shape.
He might only be accused of being out of position in the first half when he rushed back several times to the left side of the defence when under attack. Only after you changed your shape in the second half that he played as a left forward, and was never far from the touchline since then, if that is what you call positional discipline.
I think a lot of complex strategy are applied by a football team at the premier league level, much more than just picking a standard formation and players to fill the spots. Top level teams are too advanced to lose shape, certainly not because of one rogue player playing out of position.