Removal of pink wards actually made invisible champions unbalanceable.
Previously, if you had pink wards, against invisible champions such as

, there was clear counterplay: you could instantly down a pink (at the cost of a slot and 75 gold) in battle to reveal them, which puts the fight on an even footing.
Now, with the removal of pink wards, we've essentially found that invisible champions (not camoflauge champions like
that mostly use invisibility to evade wards) they will either be OP (Shaco having 2nd highest win rate in the jungle, Vayne having 4th highest win rate in a lethality/utility ADC meta) or useless (none of them so far because their numbers are too high, but if they get number nerfed, this is where they go).
http://champion.gg/champion/Shaco/Jungle http://champion.gg/champion/Vayne/ADC
This is because if they get ahead, they can 1 shot anyone with absolutely zero counterplay, both strategic and tactical: you can't even run away from them or stay out of their range, since they can invisibly gapclose to you. If they are behind, they are absolutely useless and use invisibility to escape only.
Without any form of invisibility reveal, you cannot peel for your ADC, you cannot engage them, you cannot disengage them. There's nothing you can do about it if they get ahead.
did grant (or still does???) grant True Sight of invisible units that the ghosts encounter. But it actually has good counterplay. The invis champs can see them coming, can try to outrun or outplay them somehow. Effects that aren't immediate would go a long way toward making the invis champs less frustrating to play against.