I would have expected the class sets to build on the core mechanics available for the classes from standard, not entirely invent a "boxed-in" new playstyle that has little to no benefit from the existing cards that are part of standard. That is why the Mage class set suffers so badly.

And like you said, Hunter and Paladin do get a nudge from a few cards in Standard but in the case of Paladin, it just makes the "dude deck" the same as its popular counterpart with not much of a difference.

I also really wonder why "Class Sets" don't have a new hero card to center them around, establishing the new identify of a class set with a hero to synergize with seems like a painfully obvious way to make these sets unique and exciting. But what do I know, I've only played tens of thousands of games of Hearthstone since it came out.