By the way:
Papelbon 2006-2009: 1.74 ERA, 271 ERA+, 2.41 FIP, 0.917 WHIP, 10.6 K/9, 5.20 K/BB, 151 savees.
Rivera 2006-2009: 2.03 ERA, 223 ERA+, 2.60 FIP, 0.914 WHIP, 8,8 K/9, 6.78 K/BB, 147 saves.
If you understand the meaning of the word "arguable", then I fail to see how you can flat out state that Rivera (or anyone else) was conclusively superior to Papelbon during his four-year peak.