I've always been a Zombie main since I started playing this game, and I disagree with you.
I reached Ultimate League for the first time on this season with a Zombie control deck, so they are definitely not weak.
I can't disagree though, that the plants got many insane cards, but that doesn't mean that the zombies didn't got pretty nice cards too. (Like Alien Ooze and Triplication).
I will leave you the link for the deck I used, in case you are interested.
http://answers.ea.com/t5/General-Discussion/The-Ultimate-Control-Deck/m-p/6142302#M5707
