I love Lamela, the roll of the foot over the ball, the tricks, the subtle passes, he's great to watch. Yes, he doesn't score half as many goals as you want, can be frustrating when he loses possession however the reason he's picked is because he's actually a very well rounded player.
When you consider Poch puts high emphasis on fitness, its no surprise Lamela is selected because the guy has a great attitude, keeps going and never drops his head. And when you consider he's an attacking player, he actually does a huge amount of defensive work (defensive stats are impressive) he gets back, covers ground etc.
Going back to the frustrating part, what i find more frustrating than players losing possession, is players who give up. And that's why he's selected, hes a team player. Much like Sissoko who is prone to losing possession, his fitness is incredible, and hes a team player. Honestly, if we want to win the league, its all about teamwork. I honestly think this might be Lamela's season.