OR they do medeocre damage and have the largest CROWD CONTROL. There's more than one way to balance a magic class in a game, and not all of them have to be greatest DPS.
RO seems to be taking it to the route where melee classes do the most damage up close while magic classes are crowd control. The problem then is that we get skills like Dragon Breath which...yeah.
Frosty = Greatly slows down targets... if it sticks. Base chance is 80%, but that's with 0 MDEF and monsters being the same level as you (i.e. not stuff you level on). The actual chance is often below half. The balance patch is further nerfing the base rate down to 50% - good freaking luck getting this to stick on stuff you're fighting for exp.
Cursed Circle = Complete and total shutdown of 15 enemies. Cannot be resisted. Does not break. Free kills for your party.
If there are many ranged targets (where Cursed can't reach them all at once) or there's a *huge* mob (huge enough that it's better to slow 1/2-2/3 of the mob than shut down 15 monsters), Frosty *may* win. Anywhere else, Cursed Circle is very clearly the stronger crowd control, and with the 80->50 nerf, I think it's safe to say Cursed wins always.
Compare White Imprison to Manhole, and you'll notice something similar.
Manhole vs. WI:
Unblockable vs. 65% chance to work vs. equal level and 0 MDEF.
2 second cooldown vs. 4
3 points to max vs 5
Removed by a 5 SP spammable Priest skill vs requires ME (although neither matters in PvM)
Choose between aiming directly at an enemy or planting it in their path vs. must aim at a target
Requires a useless Rogue skill to unlock, but 0 SC prereq points vs. requires 3 Lock prereq points in a rarely used spell
Hard cap of 3 active targets vs. soft cap of 3 active targets (Strings increases this to 5, but that's if nothing ever resists it, and without Strings, you're unlock to even get the 3, while MH can guarentee that)
Does no damage vs. does trivial damage (2k at max)
Target cannot be harmed vs. some skills work, but they break the effect and thus merely give you a chance to break the effect early after repositioning.
Both can be used on self as a desperation defense move, but WI is self-only, while Manhole can be jumped into by allies if needed.
WI has a couple of advantages at the end of that list, but it's pretty clear which one is overall better.
Of course, WI and Manhole are largely moot in PvM since the idea of a dungeon built around small groups of powerful monsters instead of swarms is gone, but I wrote that second part on the assumption that future instances or something will restore that style of play.
If the goal was to make the Locks trade damage in favor of being the ultimate in crowd control, why are both of their signature CC moves inferior to melee class' equivalent moves... with one of them about to receive an additional nerf to make that gap even wider?