Does that last ability affect more than like 3 cards in all of Magic?

Forecast exists as a mechanic. And the reason activated abilities from your hand are so rare is than only black can answer them (via discarding cards.) The ability is also needed to make the card feel black.

cycling, reinforce, etc.

@amuseum: Well, yes. But you're already discarding to get those effects, so there's no benefit.

I was going to suggest exiling from hand instead. But then I realized that a cycled card would be in the graveyard when the ability resolves. But... wouldn't this card be more relevent if it exiled cards with activated abilities from the graveyard anyway? Exiling from graveyard is still a black ability, so the cost would be fine. And it seems like a good way to get rid of a Dread Wanderer for good...

You could even use less words all around: "Counter target spell, activated ability, or triggered ability. If the ability of a permanent or card in a player's graveyard is countered this way, exile it."

You could even alter jmgariepy's wording to reference "card in a player's graveyard or hand" instead; this way the minor interaction with forecast etc. is not lost, but the effect is less narrow.

I like that exile can be used as a catch-all that will be most satisfying.