I kinda have to agree with this guy. I have been battling alot at gyms tho.
I got my Dragonite 3375CP Steelwing/Hyperbeam and another Dragonite 3375CP DragonsBreath/Drangon Claw.
The thing I found interresting was, that I was beaten by a Snorlax 2200CP when I was defending with my Steelwing/Hyperbeam setup. He didn't stand a chance against Dragon Claw. (Spells are same type)
As of I wouldn't recommend the "DPS" guidelines from Silphroad. Or ATLEAST take a look at the Duration MS for the spells.