EneMG has got HIDDEN Built-in PVM bonus to his damage, exactly 20% basic wizzardry damage.
His Staff lets say around 100% rise, doubles that hidden bonus to 40% and more with better staff.
EneMG has got more stats than SM with better min damage formula and the same max damage formula for energy.
All this combined makes EneMG damage higher of around 80% than EneSM in PVM on the same skill.
No matter what items will you get on your SM you will always be HALF of EneMG damage output.
I Hope it clears the situation for you now.
Admins should be informing that to players when they added these hidden modificators.
Regards Ronin