Okayyy, well, just to clarify, I was able to beat the gurubashi bosses with only using the energy pots and a couple of health pots at like level 10-11 , if you want I can let you know the method I used. It just felt like it was an easy way to go through the mobs both as a mage and warrior .
It was a matter of not letting them do damage. For e.g - as a mage , cast frost nova , cold blood , energy pot , nova , cold blood , energy pot etc . and slowly the boss died. As a warrior I don't recall what I did but there was some sort of a similar method. Maybe for future references a limitation of 2-3-4 energy pots can mitigate this and only be acceptable for onyxia etc :D