Runes of Magic US / AU

Rotation might have something to do with that. IMO a wl/ch rotation would be:

Buffs - including set skill buff Dark Soul Essence

{{ Rage Sublimation
WPB
Saces' Impulse (every 60 secs)
Rune Energy Devotion (as available)
Ruthless Judgment (until out of psi) }} Do this section every 20 seconds

Electrocution (to get the debuff)
Energy Influx Strikes (when you have the debuff, and as available for more dps)
Weakening Weave Curse (for the debuff)
Warp Charge (for the buff, and as avaialble for more dps)
Heart Collection Strike (as available)
Surge of Malice (as available)
Puzzlement (as available)
Psychic Arrows (when everything else is on cooldown or you have all the bfufs/debuffs needed - if you are fast enough (or use diyce) this actually does happen)

Whether wl/c or wl/m is better on boss fights depends partly ( or greatly) on the other players in group. Remember that wl/m has raid wide warp charge buff (assuming ppl are in range of the casting warlock/m) and puts soul brand on boss increases fire damage (mage dps, w/m dps) by up to 36%.

Mrpushpop almost always has other well geared w/m or mages in group making his soul brand very valuable/powerful, and being near to other dps makes warp charge on wl/m another powerful dps increase tool (increase for the raid/group, not the player specifically). In these cases, wl/m will always contribute more then a wl/c can, and warp charge by itself might make wl/m more useful compared to wl/c in cases where all other dps are equal to or better then the wl/m.

In general, wl/m also has the silence and root/interrupt of lightning. wl/c gets electrocution but that means wl/m has one extra "disabling" skill then wl/c does, unless i'm forgetting something.