Mesmer has every bit of utility you could ask for topped off with: clones, hard immunity and thief level frequency of invis if not more. Sustained damage is excellent and burst is instant making it harder to counter than most other classes/specs. This is no secret and is abused to the point where ranked teams are running 2/3 and even 4 mesmers. I'm only high gold, however my plat guildies (some previously legendary) say the problem doesn't stop in my league.
It's so oppressive to the point where I'd rather pull a fish-hook out of my stomach with a string than continue to play this game with its current surplus of mesmer BS.
Something needs to be done about it. Many things could be done, but capping their clone count at a lower number than it currently is would be a good start.