First I just want to say I absolutely love the art on this card, maybe my favourite in the pack. The whole theme of the card is just fantastic all around.
That out the way, I think the most obvious comparison for this card is Logical Reasoning as they are the two cards in the game that can testlessly discard a treachery in play. I think when Alter Fate was revealed a lot of people saw it as a less flexible Logical Reasoning, due to them both being able to discard one of the worst treacheries in the game and Logical Reasoning having the added benefit of horror healing, but I dont think this is entirely fair. Alter Fate is fast, useable outside your turn and doesn't require you to be at the location of the player you're helping. Not to mention there are a fair few pretty nasty non-terror treacheries you can hit.
I think Alter Fate really shines in the second half of Forgotten Age where it can deal with Words of Power, Yithian Presence, Entombed, Creeping Darkness (surprisingly) and Frozen in Fear when you have 2 willpower, all of which can require a significant investment of action or cards to deal with otherwise.
I also think it does a lot of work throughout Dunwich where between Arcane Barrier, Locked Door, Cursed Luck, Beyond the Veil and the campaign's liberal use of the Striking Fear encounter set, every scenario has at least one target and usually several.
Ultimately the value of Alter Fate is very dependent on the campaign and the investigator choice. If you are playing through Dunwich with a group containing multiple low willpower investigators they are likely to thank you for running it. If you are playing Forgotten Age and some of your investigators are worried about the agility test on Entombed it may be worth it.
A few investigator specific notes:
Father Mateo can take this card, as it is Blessed, and since its a spell he can dig for it with Arcane Initiate. This is dubiously worthwhile as Mateo has lots to spend exp on and can already take Ward of Protection but it could be interesting in a very supporting control focused build.
William Yorick has only medium values for both agility and willpower, which makes him vulnerable to a lot of the treacheries that Alter Fate is useful against.
Calvin Wright may specifically find it useful for dealing with Curse of Yig and Dreams of R'lyeh which can be brutal for him, as a form of virtual damage that bypasses and soak he has in play, though he can also play Ward of Protection which does a mostly better job.