He never seems to be in a good position defensively. Think he will get murdered by good teams for his lack of positional sense.
Tough to say, his strengths are obviously at pressing high, and vision. But I think he gets unfairly called out for his defensive abilities.
Check out his dashboard from the Soton match:
From a defensive perspective, the green + signs are ball recoveries, the green Xs are successful tackles (the orange ones are unsuccessful), a green O is a clearance, a green diamond is an interception. Lastly, the 2 black triangles on the edge of our area are fouls he committed, and the 3 white ones were fouls committed on him.
While there isn't any way to truly measure positioning, if there were mistakes that led to shots or goals they'd be indicated by large yellow or blue octagons. You could argue the 2 fouls he committed in their attacking third were because he was out of position. I could take a deeper look to see if any other Everton players had more activity in what would normally be his area, but on the whole, Sidibe is just fine at playing defense.