He is a good player. Genuinely two footed. His first touch is like Alli's, on the surface both lose the ball with their first touch but placed into context they are the ones that are taking the ball on the run, trying to turn their first touch into an opportunity to create space or aim it into a space between the oppo defensive block. This is far harder to do than just bringing the ball under control at your feet. The best at doing it in our team is Kane. Eriksen and Lamela are slightly better at it too but under pressure they too lose the ball frequently from their first touch, what both do very well however is compete to win it back almost straight away. This is what Son doesn't do (yet, crosses fingers hopes he can).
In fact this is actually a feature of our play and has been so successful for us, we win the ball high up the pitch. Think for a bit, in order to win the ball back and high up the pitch, first you have to NOT have the ball or first you have to lose the ball. There are times we want to lose the ball in the "right" areas. Which brings me onto Son being dispossessed frequently, there is nothing wrong in this, as we will regain possession of the ball quickly when he does (as mentioned above I would like to see him do this, he is simply not aggressive enough), we have scored goals directly from Son going on a run, drawing and committing a couple of players to him, he is tackled but that tackled is quickly followed up with another player winning it back for us and taking advantage of now having a couple of defenders out of position and creating an overload for us in and around the penalty box. (Think of the reverse of this, how many tackles do we make in our deffense, hardly ever, it is rare to find us being caught in possession of the ball in and around our penalty area because are defenders don't dive in or commit themselves anymore). So in short, it is a deliberate ploy of ours to lose the ball, to commit defences and create overloads and therefore create opportunities to exploit. It is all about the 2nd and 3rd phases after we have lost the ball and their defence is committed/turned/out of position. Embrace it because it is deliberate, it's what we do.
He desperately needs to improve and be more committed in the challenge in order to contribute to the teams ability to winning the ball back. I am not expecting him to turn into Alli or Lamella here but expect him to be more like Eriksen, who let's face it bottles a challenge too but he is becoming more terrier like and has won the ball off a defender to set us on our way to score on a few occasions (Norwich, springs to mind but certain there are others).