Ok, let's see.
Starting with the anchor/CDM; Biglia. He's by no means great, but great anchors are extremely rare. He's done an alright job as distributor and "balance player". The midfield would improve with a better ball-winner and playmaker than him but you can form a strong midfield-3 with an okay anchor like Biglia.
Kessie. His passing, finishing and on-ball decision-making have been very frustrating to watch at times. But he's the only midfielder we have who's athletically up to standards. The only workhorse mezz'ala. And he has more time and room for improvement than Bona. We do need alternatives though. His spot on the team shouldn't be given either.
Then there's Bona. As the advanced mid we're sacrificing the defensive solidity of a proper midfielder for the technical abilities of an attacker. With this in mind, Bona's late runs are fruitful and he's a very good dribbler, but he doesn't have the passing skills or pace or team player mentality to make more out of it and he doesn't cover as much ground as you'd expect from someone in his role(because he wastes his energy on dribbling which rarely gets us anywhere).
Has he been starting undeservedly at LCM? No. He earned it by showing more awareness and positional sense than Hakan, who struggled to make any impact at all when he was fielded there earlier in the season(he turned around his season when Rino moved him up to the attack). But we can do a lot better than Bona. It shouldn't be too hard to find advanced or B2B mids who are better than him.
well you talk out of subjective opinion i talk numbers in serie a.
Bona has 8 goals and 3 assists while hakan who is playing in more advanced position has 2 and 4 and kessie playing similar position has 5 and 3(Bona wins)
Bona success passing percentage is 88.1, Hakan is 84.1 and kessie 84.6(Bona wins)
Bona average rating is 7.07, Hakan 7.1 and kessie 6.8( hakan wins with very small margin)
so it is not that we have world class midfield, so i would consider get off his ass till we do and see other position which needs to be filled.
i believe Bona best position is in the LW, as he is much better in the offensive more than the defensive and can dribble and score. Hakan can play in the LCM as he cover more ground and he can't dribble, i believe the 2 players didn't perform because they are not playing in the position that can fulfill their potential.