Yeah, Pack Rat's problem is that Plague Rats with Flash is a really solid card in a Rat tribal deck, and Pack Rat makes your deck a Rat tribal deck. It doesn't help that you need a board wipe to deal with it effectively, since any of the tokens can rebuild the entire army.
There's a reason that most token-producing mana sinks are closer to Jade Mage.
There's a reason that most token-producing mana sinks are closer to Jade Mage.