Lets see what the weakest class against each of both can do against it with a single card.
walrus still costs only 5 and if you happen to be Solar Flare you can do Exactly three things: Three Headed Chomper, Carnucopia or Smash Pumpkin. Both Plant solutions Cost more than the Walrus itself and Pumpkin is at the same Curvespot. So you got 1 reasonable 1-1 trade option with the weakest class against walrus.
now for Counterplay against Oak: EVERY. SINGLE. ZOMBIE. Literaly every single Zombie you can play can block the damage for you and a vast amount of zombies can also kill the oak. Obviously some cards are more efficient than others. but seriously. you can always just chump-block it.