Always told you the problems were mostly due to injuries (and confidence actually...)
As a profile, he's exactly what you need now, someone who brings speed and breaks lines, in a team that sorely needs that.
I don't think confidence was the issue per se. If anything, he has always been cocky and overzealous, leading to dribbles when he shouldn't be dribbling and attempting stupid risky passes in the wrong parts of the pitch, amongst other things that were frustrating to watch.
His problem however is he lacked the right amount of prudence and correct decision-making, two things that tend to improve with time and obviously with dedication towards your craft (I suspect he has been actively ironing out his faults).
Football isn't just what you can do, but also WHEN you decide to do those things, especially in relation to your team, and in the context and moment of the game.
If the team is moving the ball around trying to take the air out of the opponent because we grabbed a lead and we are trying to assert a bit of dominance over the opponent, than trying to dribble out your man and create danger opportunity at the risk of losing possession moves down the line of priorities, at least momentarily.
Dembouz is perhaps beginning to realize that just talent and skill is not enough to be a top player, you also need to use your head. Good footballing IQ is a must, and that means sometimes sacrificing your desire to always excel and produce things out of the ordinary, as great players tend to want to do. That's maturity.