Sure they do much damage but they need a HUGE discard to reach that damage.
Look at Charizard. You do 200 for 5 Energy. That is 40 damage for each energy. But you also got to discard them. Without an energy accelerator, you do an average of 40 damage a turn tops.
Compare to Flygon Ex. He does 80 for 3 energy. That is less as 30 an energy. However, Flygon can hit constantly for a solid 80. On Average. And he doesn't need as much charging time as Charizard.
Then there is the fact that without having to discard energy, you can charge up benched pokes.
So no, Lugia and Charizard Ex aren't insanely powerful. You want pure raw power? Take a peek at Salamence Ex (Power Keepers)