Well, I don't have a m/k, I am m/p and m/s, but I kind of agree with everyone.
The reason why Xaldyn is saying that m/k does just fine in a boss fight is (at least as far as I can see it) because a mage's boss rotation is almost identical across all class combos. In that sense, a mage is a mage is a mage.
Flame is the skill we all use in the burn phase. Most boss fights that aren't cutting-edge content are less than 30 seconds in duration, and if you have three different mages with three different second classes, you're all casting the same things mostly and there's little variation in dps output.
Now that's really a simplistic view of the issue, as there are other factors at work too- some combos have good passives and buffs like m/p (Essence of Magic, which if we have a m/p in party, we all ask them to buff us so... yah). M/S has a self-only crit buff and a short term speed casting buff which helps a little. M/P also has the elite skill Explosion which makes Outburst happen more often, so that can cause them to burst dps higher. M/W has all kinds of crit buffs and passives, and that's why they can burst so high also.
M/K lacks self-buffs (iirc) and so it has less dps potential on paper. In reality, when we're all firing away- it doesn't make much difference. Learn to use your buffs correctly and cast them at the right times, and you'll find yourself beating equally geared m/s's on the scrutinizer if they get sloppy during the buff phase.
Gear correctly and buff correctly, and you will be fine.
And there is no reason at all to get attached to a combo- we have third classes for a reason. I use m/p in some instances and m/s most often. Just depends on what we need, and what I feel like. Try out m/k and see if you like it- it most assuredly is beastly in PvP and it can hold it's own in PvE, although other classes get better buffs and passives (and I just realized that that isn't true- you are getting Enhanced Armor, and that survivability may end up winning you first on the scrut even though EA doesn't boost dps. You can't dps when you're dead

)
Mage is less about the combo and more about how well you gear and play the combo you pick.