Prior to last season, he had 20+ goals in all competitions for 2 years in a row, and lit it up for 15 Goals in 23 matches in the 2nd half of 2008/2009 when he transferred to Sampdoria.
Here's some numbers for the sake of Comparison.
In all Competitions, from January of 2009- Last Season, Pazzini scored 67 Goals in 146 Matches, which is a scoring rate of 46%.
Taking his piss poor season last year out of the equation, those numbers are 59 goals in 107 matches, a scoring rate of 55%
Pazzini's last 3 seasons, including last year, he has scored 52 goals in 123 matches, at a rate of 42%
Matri, in 3 full seasons, has scored 43 goals in 108 matches, which is a goal scoring rate of 40%.
Now, in the last 2 season with Cagliari/Juve combined, he has scored 30 goals in 69 matches, or at a rate of 43%
In the last 18 months with just Juve, he has scored 19 goals in 46 matches, at a scoring clip of 41%
Just going off of the raw numbers, it is pretty evident that Pazzini is indeed a more prolific goal scorer. Again, Pazzini had the benefit of Cassano for what amounted to 2 full seasons, but it can't be discounted that his goal scoring rate actually improved in the 2nd of of 2010-2011 when he went to Inter.
matri has not had the benefit of a Cassano type player, as Vucinic is possibly a step below, and he has yet to play with Giovinco.
However, Pazzini has not had the benefit of playing with Vucinic and/or Giovinco either, and would be coming to a superior team with Juve.