Going Viral seems like a real pain in the butt, from a Plant Hero player's perspective, sure.
But it's not quite as good for the Zombie Hero as you might imagine.
Shuffling three more GV cards into your deck each you play one can mean that, eventually, you're drawing another one practically every other turn. In the late-game, GV might be all you get, when you really need some more zombies to get into play.
Plus Zombology Teacher is not a strong card, and it becomes a target for elimination as soon it appears.
The odds of a player being able to play two (or more) and keep them both in play long enough to get some cheap or free GV in play is rather small, if you ask me.
And yes, as @patdk75 pointed out, without Frenzy GV doesn't have much else going for it. I would put some other 3-cost card into my deck instead if it got nerfed.