5.1 Malevolent Gear has a higher ilevel than 5.2 Malevolent Gear.
5.2 Malevolent Gear has more PvP Power/Resilience than 5.1 Malevolent Gear.
5.1 Malevolent Gear
483 ilevel (491 with 2/2 upgrades)
~30 ilevels of PvP Power and Resilience
5.2 Malevolent Gear
~36 ilevels of PvP Power and Resilience
In the end, the effective Ilvl of patch 5.2 and 5.1 Malevolent gear puts them at about equal. The reason for lowering the item level and increasing the PvP stats for the 5.2 version of Malevolent gear is because we want players to run 5.0 LFR, this means that the Ilvl of honor gear needs to be lower than the entry requirement of 483. The result of this was lowering the Ilvl (stats) of the gear, but increasing it's PvP power and resilience to compensate. That difference in power you feel is going to be extremely prominent, is actually quite minor.