The same can be said for legendary cards, too: I don't have any of the great legendaries like Cairne or Sylvanas or Ragnaros, so we could argue that I shouldn't

The same can be said for legendary cards, too: I don't have any of the great legendaries like Cairne or Sylvanas or Ragnaros, so we could argue that I shouldn't be matched against those people—but, when I do go up against those cards, I find that I have about the same win rate as against any other deck. Probably slightly lower, but not enough for me to really notice. Some of the Naxx cards are definitely cool, but, like all the other cool cards, none of them make or break the game. Sure, Sludge Belcher is the best taunter in the game right now, but it's only slightly better than the Sen'jin Shieldmasta, which is still a fantastic card and is still absolutely free. Access to good cards is helpful, but nowhere near as important as strategy and experience. Heck, go watch some of those free-to-play folks who start fresh accounts, never pay money, and still rank waaay up. If you refuse to concede when things look bad, you might be surprised by how well you do. (Also, the Naxx single-player content is excellent. Even if you choose not the use the rewards, Naxx itself might still be worth the price.)