For the best, answering the title. You may say Infernape Lv.X is broken, doing 150 with 2 Fire Energies. But, a Infernape EX will be very more broken, with ~150HP and discarding many Energies. Infernape Lv.X has 120HP and you're not sure there are 2 Fire Energies in the top of your deck.
But the very bigger advantage is the ultimate combo:
* Infernape Lv.X with 8 [R] attacks and discard 8 [R]
* Attach 1 [R] to Infernape Lv.X and pass
* Attach 1 [R] to Infernape Lv.X and attack
So, you Knocked out about two Pokémon in three turns.
The Empoleon line is somewhat ineresting ... bench hitting attacks at most stages & the level x can do 80 to anyone active or bench. So spread damage and then selectively KO.
Overall I don't see *most* of the DP cards being all that. I do see an overall slight trend of increasing power where more DP basics have more HP & better attacks than you see on average in other sets. More of the stage 1s & 2s have some slight increases in HP, for instance Machamp (dp) has 130 HP vs 120 for the (pk) & (lm) versions ... yet I still think that Machamp (lm) is better overall (I *love* that first attack) & Machamp (pk) can do more damage vs EX pokemon. So it's not a given that DP is "overpowered".