Certain effects make you discard from top of your deck. Now, my initial thought was that weaknesses with Revelation discarded this way would get put into play. But then I read the rules, and it says that when weaknesses with Revelation would be drawn into your hand, then they get put into play instead. So, despite the 'Grim Rule', it would seem that weaknesses that go straight from deck into discard pile would not enter play as per the rules text under Revelation?
Your last interpretation is correct. A card "discarded" from the top of the deck does not count as "revealed."
Another thing to keep in mind: the Grim Rule is not a principle for determining the correct answer for a rules question. Instead, it is a principle for resolving questions that arise in the middle of a game, when you don't have time to look up the correct answer (or post on BGG and wait for other Geeks to weigh in ).