Quick look at stats for both suggest Moorman has been better in most categories, over about same number of games and kicks:
Powell = 19 returns for 14.73 yd average, 1 TD, 1 inside the 10 yd line, 5 TB and 5 FC. Powell's average is about 6 yards more..
Moorman = 12 returns for 11.25 yds, 0 TD, 3 inside 10 yd line, 3 TB and 9 FC. Both have 10 kicks iunside the 20.
The Cleveland game sealed Powell's fate. Moorman has done pretty much what they needed, which is to stabilize the return defense game. Clearly, his time here is over after this season, in my opinion.