Elf decks already played the Whisperer, so you shouldnt have a problem playing both
Medusa makes it very difficult to get big powerhouse cards out with hopes of them lasting long enough to make an impact, and thats why her impact on the game is still felt to day several sets after she was first introduced
If your opponent casts a bigger creature, you cant steal it, so your options are a little worse and you might need to rely on your following spell to answer it, but if your following spell is a Wicked Wolf, for example, no matter what they cast, you could turn it into a 3/3 and then use the Food you created the previous turn with Oko to kill their creature with your Wolf after making it a 4/4
A two-mana 3/2 that enters tapped would already be a decent playable, but the additional effect here is quite good
Sometimes you don't want a card to solve itself, and other times Occam's razor proves true, and you just want more life-gain-matters effects in your deck