Ignoring any undiscovered new tier 1 decks that may come from TGT which I doubt will happen, none of the cards in TGT that you would replace in an existing deck are a complete upgrade over the replaced card. At best it would just be a side-grade which is better in some situations but worse than others. An example would be replacing Zombie Chow with Darnissus Aspirant in Druid. Sure Aspirant has a great effect but it's 2 mana whereas Chow has the advantage of being only 1 and can stop aggro immediately in it's tracks, and also help fill out awkward mana curves.
This is now getting into personal opinions and predictions but I think there are quite a few cards that would fit into existing decks that either have no other counterpart in that deck or are better options than existing options.
Example is Holy Champion. Any deck running Holy Novas and Circle of Healing should run this card IMO. It's too huge of a threat to leave alone. People don't let Light Wardens live a turn because they are that scared of the card, they should be twice as scared of Holy Champion. Priests that run this type of deck don't use Shredder so you can't even say "oh but Shredder is better than this card". This card provides the offensive pressure the slower Priest decks needed to possibly push them to the next level.
Healing Wave is another example. Shaman class as a whole is very fragile and one of the reasons why they can't play a slower game is because they simply lack the heals or defensive tools. This card combined with Ancestral Knowledge and Elemental Destruction provide Shaman with the tools to play the slower game. Even if the slow Shaman deck doesn't work out, Healing Wave is a great include even in Midrange Shaman for the burst heal against aggro.
And then stuff like the Lightbane/Darkbane cards which are a fine fit in aggro/buff type decks that can get out of control even early in the game.
In any case saying that not even a single card would be worth owning from TGT is hyperbole IMO. I would legit take a bet on this.
From the looks of it, it looks like Rogue and Shaman got significant improvement in general with TGT. I could be wrong though. I'd love for more cool stuff for Rogue.
Unless Pirate decks are at least tier 2-3 deck... Rogue probably got among the worst class cards in the set. Shaman is definitely top 2 in improvement for TGT though.