1. Depends on the fight - yes for Patch, no for Heigan for example Must admit I've never examined our dps parries.
2. It causes next swing to be faster only if a certain period of time left on swing (I'll leave someone else to explain the details, cos I'll only get them wrong). Swing is directed at whoever (hopefully the tank) the boss is currently swinging at. Worth noting not all bosses are parry-hasted, the really really big hitters tend not to be.