Not a joke to most of us. When grouped you should be killing nearly twice as fast. People are complaining enough about 300% XP, can you imagine if it did stack with Rest at 500%?

Honestly it is just right if you ask me. Same as having 1.5x rest XP even if you level none stop. Then to top it off by the time you get to 60 you will have most likely 1 1/2 bars of rested XP from the get go.