LordZelkova touches on an interesting idea: why not try to solve this conflict by means of role-play?
Perhaps Engineers could have a "place charge" skill that would have a chance of breaching an LWC'ed chest. The skill would cost money to use, or use rare reagents, and the chance of success would scale with level.
And perhaps the rogue classes could have a "pick lock" skill. This skill would also cost money to use, or require a rare reagent. Success chance would also scale with level.
If one wanted to be really "hard core," the cost for an LWC breach or pick attempt could be a character's experience... Say, lose a level or two. This mechanic, combined with the way the chance of success scales with level, could insure that the rate of successful breaches/picks is reasonable.
Furthermore, one could take the concept a step further and make a loss of experience integral to creating LWC chests in the first place. Want to LWC a chest? Each chest will cost X experience.
Or perhaps only Engineers (and possible Rogue classes) can make LWCs. Upon creation, the chest gets a "key." Whoever is holding the consumable key upon final activation becomes the owner of the chest.
Going even further, perhaps Engineers or whoever could create a "Masterwork Locked Chest," too. This would be a truly uncrackable chest, but would come at the cost of a permanent level cap reduction in the creator's combat class or profession. Or both. This could create an interesting balance of playstyle: players who insist on having truly safe storage could only do so at the cost of having their level cap nerfed.
Maybe make it harsh, like 5 levels per chest. That way, a player could have 12 truly safe chests if they were okay playing as essentially a Lost Soul.
Anyway, I'm just spitballing ideas here. I'm not particularly advocating for any of this, as I don't really have a dog in this fight. I rarely own anything worth stealing!