I need more persuading to believe that Marrone is not suited for Bonucci's position. The name "Javier Mascherano" keeps popping up in my mind.
You know that Mascherano was arguably the best out-and-out DM in the world when he went to Barca?
When has Marrone ever shown any real defensive ability?
And, even as good as Mascherano is at one-on-one defending, when it comes to positioning and reading the game it is continually apparent that he is not a natural CB.
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Also, Mascherano is very quick, so he can recover from positional errors at times.
Marrone doesn't have that.
All in all, any comparison between Mascherano and Marrone is utterly ridiculous.
If you must try to clutch at straws to try and convince yourself Marrone could have a future as a CB, at least use De Rossi as your comparison.