Well for one....
The whole Melo is a DM and Marchisio is a CM argument is redundant. Why compare the two or compare there impact if at the sight of stats you shy away to that argument ?
Two, marchisio is highly underrated , sure he's no vidal but he scored 4 goals this season and I believe 2 of those were at crucial times. Talk about clutch? He's also clean in possession if there is anyone on the team I would bet on to not lose the ball it would be claudio..now if only melo had half of his ball retention skills he wouldn't give the ball in our final third trying fancy back-heels. Not taking anything away from melo though..
Apparently melo was supposed to be a good long ball passer...Besides his pass in the World Cup I've seen very little of this, and I don't count his passes that switch play as good passes because they are really easy to do. True defensively he was a beast, almost like a wall in front of the defence. But his ability going forward left a lot to be asked. Defensively, Marchisio tries his hardest, no he doesn't win every ball but he likes to fight something I praise him for.
At the end of the day Melo and Marchisio serve seperate purposes, neither was more important than the other in finishing 7th (which btw isn't an accomplishment). Sissoko could have done melo's job just as efficiently. Credit for saving this season goes to Quagliarella and Matri. Quag was our rise and downfall, while Matri helped stabilize a sinking ship. Which Melo didn't help with his rash actions during the campaign. Oh yeah, one more thing! (jackie chan granpa voice) . If Melo had his head on right he would be a much better player, no reason to moan to the media about a bad season. A true leader would have called a team meeting during the season or something...