Yet again the issue isn't with DCE, it's with the attacks themselves. Sure, DCE can 2HKO everything on Zoro, but only because of how Zoro's attack works. DCE can also do 20 damage when attached to a Slugma.
It's not DCE that's inherently broken, it's the attacks and their unfair cost.
Correct, but DCE indirectly is the issue. Zoroark is just symptom of the card existing. Remember, X-Ball like attacks are a problem too because they can use it. Gardevoir-GX is easy to setup and can get five energy in a turn with DCE. Zoro isn't the only good DCE attacker. You have to remember that DCE wasn't designed to be used by every type in the game, kind of how like in the main game, Surf is more powerful coming from a Vaporeon and not a Lugia.
Since the attack cost won't change, banning DCE is the easiest way to balance all those cards. Remember they can make a DCE Prism Star if they really need to keep it around.
These attacks can be very powerful, but not necessarily. Look at Nosepass BCR! These attacks would be too OP for a single energy attachment, while they would be unplayable for 2 energy (not CC). DCE is necessary to give attacks a 1.5-energy cost.
A lot of cards are bad. Zoroark could be [D][C], but it isn't.