I don't think the Burn condition has ever been 10 damage, but if Burn did exist in the Neo era, it might not have been 20. Oh, I misread the attack, my bad! I actually think the original attack was pretty balanced, perhaps just needing a few tweaks to err on the side of caution. I think that it would be better balance-wise if you could only Burn a single Pokemon per each use of the attack, like in a [R][R][D][D] attack, discard two [R][R], a Pokemon is Burned. However, I'm not too sure if the idea behind the attack is to have multiple Pokemon Burned at once, as this method of balancing would entirely change that. Just that in the modern era, damage boosting cards (such as Special Energy) do not boost attacks that don't have a base damage.