I dont think there is any correlation between midfielders and goals as an indicator of making them more efficient or damaging. Truth be told, dominant midfielders who have 30+ posession games are usually on the winning team (with exceptions)
Boyd's 30+ posessions have a minimal impact on the outcomes of our matches this season, added to the point that he doesnt often get tagged, it shows what little respect the opposition have for Boyd.
Boyd can have a 40 posession game, but where his efficiency is 40%, he might aswell not even be out on the park. Cross gets his hands on the ball, sometimes nearly as much as Boyd. But the argument lies within both player's ability to damage the opposition with their disposal. Neither Boyd or Cross have ever been damaging and never will be.
Now that we no longer have Cooney (playing as an effective midfielder), Eagleton, Johnson, Gilbee (is tired & slow) etc both Boyd and Cross have been exposed. Thats where the problem lies within. Griffen plays a lone hand and without the follow up support from Boyd and Cross, we have few options to get the ball through the corridor