Seeing Fact or Fiction (finally) unrestricted in Vintage I think reminds me of what my whole misgiving is with Mental Misstep. The cards have more in common than being blue. A lot of the success of Fact or Fiction was timing. I had some and traded them away to a friend. I remember not being convinced that Fact or Fiction was all that great. He was determined to prove to me that it was. So he played against me with his Psychatog deck. He was a wealthier player than I was and most of my decks wouldn't have stood a chance, so I used my Donate deck, which was my best deck at the time. Maybe not as good overall as a Psychatog deck, but it had Necropotence for rocket fuel. He cast Fact or Fiction, I countered with Daze. "Ah ha," he said, "so you really do know that Fact or Fiction is a good card. You used a counter on it." I responded that yes, I wanted to counter his spell, because I didn't want him to draw three cards and put two cards into his graveyard. But now he was tapped out, because he played a draw spell that costs four mana. That cost him the game. Or maybe he would have lost anyway. But my point was that four mana is a big investment. Of course, being able to get the effect of Fact or Fiction is a positive thing. It's still four mana.
If Fact or Fiction were never printed back then and instead came out today, it would be tested for Legacy and Vintage. There'd be some talk about it on TheManaDrain and whatnot. But it wouldn't dominate or anything. I really think that a lot of the infamy of the card originates in the Vintage environment when the card was new, which was already favoring blue control anyway (in part because of Back to Basics and in part because of all the combo components that had been banned). Throw in a brand new archetype (Psychatog) that players aren't prepared to deal with, that has an incarnation in several formats, and that benefits from filling both hand and graveyard, and a card that would ordinarily be decent starts to look like a powerhouse, a staple card in dominant decks in multiple formats, decks which do not even share all that many other features (Psychatog doesn't really look like blue control, at least not superficially). And then a lot of poor players split the cards badly against Fact or Fiction, making it seem even better. But overall, stepping back from the hype, it's not that amazing.
Legacy has, for years, been an increasingly aggro-control format. It's not a coincidence: pretty much every ban other than Survival of the Fittest has been one that weakened combo, while a lot of the cards players predicted would be banned never were, and those were cards that aggro-control decks use. Meanwhile, cards have been printed that make aggro-control stronger. When Mental Misstep was first revealed, before it had even touched the format, there was already hype. I think that the overemphasis on aggro-control is the reason for this. Players thought of all the one-drops they could stop. Aggro-control loves one-drops because they come out fast and force opponents to either deal with them, using removal that sets up a clear path for two-drops and three-drops, or become crippled by them. And as with Fact or Fiction, this is a card that trips bad players up, as they scramble awkwardly to play around Mental Misstep, rather than treating it as a highly situational counter. Also, blue control was already making a comeback, in part thanks to Jace. I suspect that a niche counter that happened to get played alongside good cards got a little too much credit here.
Mental Misstep is a viable card. But it's not a powerhouse. It's nowhere near as good as Force of Will, and furthermore, I don't think anyone really thinks that it is. But it's the card getting banned because it's the victim of circumstances. Oh well, like I said, I don't like the card anyway.