The mana is not based upon your damage. It is a general rule now to not make your mana scale with damage or healing etc., because mana doesn't scale as fast as those stats. What it does is regenerate a % of your base mana relative to your weapon speed (nullifying the need to have a fast or slow weapon to game the aspect).
What we're going to do is balance the passive regen to be around the same as if you were attacking the target.
So our afkautoshot viper got changed to a passive. This is a large step for hunters in arenas. It went from being godly with the 100% of your damage, to being crap, to being slightly less crappy, to back to where it started. Walking around in circles...
But on the bright side, it won't scale with intellect anymore. Gravy.
Things are looking grim for us right now still.. But it is still beta, and there is still hope.