Your point was that Sarri needed a bigger #9 to play in a 4-3-3, not whether Mertens and Dybala are the same player. And you are right. They are not the same player. Mertens wishes he had the natural skill of Dybala.
Mertens used to play as a winger in Sarri's 433 until Higuain left/ something Dybala can't do due to his pace and characteristics - Allegri tried last year and it didn't work.
One of the things Napoli relied on when Mertens was switched to the main striker was the pace of the front three and Mertens finishing skills / in both Mertens is much superior.
Again Dybala can't/ shouldn't be played as a striker - also don't forget the CR7 factor which is actually why we're going after a big guy - he needs to drag defenders and open space for CR7 on the crosses and set pieces - we can't play the same way Napoli did with Callejon / Insigne and Mertens with Dybala up top.
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