This post at MTGgoldfish describes the usefulness of hate cards to keep strategies from overrunning a format. I rather like the idea and I think it accurately diagnoses an important tool that Wizards needs to use to keep metagames in check.
Which is why I think more removal for Planeswalkers need to be printed.
Again: for every other permanent type, there is frequent common rarity removal printed for that type. Planeswalkers are the only permanent type that have this exception: Mold Shambler and Rootgrapple are the only current exceptions to this and both of those cards cost 5+ mana, which I don't think is terribly out of line, and are 7+ years old, which IS.
WotC might think that keeping Planeswalkers at the mythic rarity is helping but that's only driving prices up. Now I'm seeing a lot of control decks that want to use Planeswalkers as their victory conditions, which means it's only going to get worse.
So; hate cards. And common level Planeswalker removal. Or at least uncommon rarity, if they want to try and keep the supertype special.