Curtis Granderson's wRC+ is 112. Austin Jackson's is 111.
The first 30 games of Jackson's career: .371/.420/.508. The last 33: .230/.276/.302. This is what happened to him last year in Scranton: he started off torrid, then slumped most of the second half. His ML numbers are almost identical to last season in Triple-A: .300/.354/.405 vs. .302/.350/.407. While those are nice numbers, one homerun isn't going to cut it with the Yankees. Even Brett Gardner has three (and a 139 wRC+).
This isn't meant to bash Austin Jackson, but to show that the guy we got in return is a pretty good player himself.
Despite Granderson batting just .246 and OBP'ing .321, his power (.455 SLG) makes up for a lot of that. And remember: he missed about four weeks with a hamstring injury. Since his return, he's slugged .529 in 25 games.
No, Granderson will probably never match Jackson's batting average, but Jackson will probably never reach Grandy's power.