to MrPrnfold, read the OP then you'll understand.
Now moving on, search through the ladders abit you'll find a couple haste mages, since I can tell nobody is really helping, I'll tell you as much as I can, because you're (in total honesty) posting on a pve hotspot ( even though it's the pvp forums, people don't get it and are generally about 2k-2.2k expirienced ) and there aren't that many helpfull opinions (apart from select few). Mages play their mastery build only in castercleaves such as MLS and Shatterplay, the haste build is just as strong however it's playstyle has little to no place in MLS or Shatterplay, whereas the haste build shines in FMP/RMP, if you can play the haste build, you aren't gimping yourself, as it's playable. There aren't many haste mages because the playstyle is harder, not because it's extremely inferior.