Different classes are different, I agree. But it should not be directly stronger than the other.
Thinking about it, Siphon Life is stronger than Plague Lord, but it's not strictly stronger. 3dmg+3heal is probably stronger than 3atk/3 armor, but it not increase your maximum "health pool". Moreover, they come with a 6mana and 10mana DK, which are also different.
The point is, there can be cards that stronger than the others; there can also be class cards that strictly stronger than theirs basic/classic counterparts, they are okay. Having a class card that is directly hit anothet class card in the face is not okay, no matter what.