mana is generally a stronger resource actually. mana is weak in the early game when you actually have to manage it, and then you buy the 1 item you need to keep it under control and then you are effectively resourceless. energy champions, on the other hand, have their burst restricted by their energy limit. they can't cast all their abilities on cd for more than a second or 2, whereas mana champions in the mid/late game can spam their abilities on cooldown for several minutes.
resourceless / fury champions are just stupid tho.