I still think he's a good player who probably isn't in a team who suit him. Like Nenz says, these are the years where he needs to grow as a player. If a good PL offer comes in we should come to an agreement, because we can find someone from within Serie A to cover the minimal role he is currently taking.
Looks like our 2-man midfield might be around for a while, so players who are ordinarily CMs in a 3-man midfield are finding themselves playing out on the wing, or even being turned into wingbacks in a 3-5-2. Lemina is doing both, and you are never going to see the best from a player out of position. To me he looks like a box-to-box CM, he's being used wide because Pjaca is injured and he has a bit of pace.
This summer we'll have the 2/3 starters in Khedira, Pjanic and Marchisio, and others with Sturaro, Lemina, Rincon, Mandragora and Bentancur on our books. The latter two might go on loan but I'd imagine at least one of the former will be sold, and with Sturaro having signed a new deal and Rincon only arriving in January that looks like Lemina. Maybe Sturaro will go too if a PL offer comes in for that madman. I'd imagine we'll sign an expensive 'starting quality' CM either way, so you end up with 4 starting CM, 2 backups, and then one versatile player who can cover different positions (currently that is Sturaro or Lemina).