Please, OP, log a raidnight and don't tell your raiders about it. Log it and link it here, there are many people that can dissect your logs and tell you just what the problem is.
At the moment locks are borderline OP even at medium skill level, and incredibly strong at near perfect skill.
I'd wager that your problem is that your lock is playing at 99% efficiency while your other DPS play at 75%.
A good lock can be 10% higher than the next best DPS even on single target, but 75-100k at the moment is 20-25% which is, for the pack of a netter word, bullshit.
Tour DPS group isn't on your locks skill level, not even near him, if they get blown to bits that hard. (Unless the stated tricks spam from rogues during profs etc.)