And there are creatures like mummies and skeletons that have special behaviour when targeted with Rewind/Eternity, which generally means they need to be rewound twice before they end back in your deck (though there's a chance you won't be able to play the resulting creature).
Nevertheless, this partially protects you from card denial.
Remember though, that if your opponent is using 3
every round to prevent you from drawing new cards, he is also hurting his own offensive ability. In case he has exactly 3 time factories, he won't be able to play any new time cards himself, since he's spending all his quanta on Eternity's ability.
Therefore if you already have more creatures on the board than the player using Eternity when he starts his denial, you still have a chance to overpower him with the cards you already have on the board. Your opponent actually needs much more than 3 time factories to gain an advantage while using this card.