Suggestion that /may/ make them more useful:
“shatter” to charge.
So the Mesmer spits out 1, 2, or 3 clones.
The initial charge of the mantra destroys the clones and gains 1 charge for each clone destroyed.
The mantra can than be use for its charges and then it would encounter its CD.
This makes them better for longer fights (not so front end loaded)
Ties their use in with the clone/shatter mechanics already in the game.
Meshes well with existing traits.
May even make a mantra healing mesmer more desireable. ( shatter to heal, rather than damage)