On two classes and with restrictions on a third. Adding it to hunters increases how often you have to deal with it by like 5x, and Invisibility is, on average, much more usable.
And I don’t know if you literally stopped reading after the first sentence, but you’ll notice the following sentence talking about how what exists/existed in the earlier expansions was already bad enough. It’s always been bad and bad for the game, but it’s at peak awfulness in retail.