Sounds about right. And that power in the hands of one person, with unlimited revision credits, seems to beat the pants off of silly ol' miracles or fate any day of the week.
We aren't aware of any other Hakutaku in Gensokyo as far as I know, but somebody had to provide that half of Keine's genes at some point. It's possible her power isn't actually that exclusive after all. That's scary.
Maybe there is some confusion at what this means. Keine's ability doesn't actually affect reality. It affects the perception of reality. This is why Reimu is not able to see the human village, because the human village's history was "eaten".
Being able to revise history indefinitely has little meaning if the target knows the truth of the matter. The revisions do not affect reality, what it affects is the perception of reality.
That said, there are several characters that are simply immune to her ability, possibly because of how it works. One of them being Yukari and another being Akyuu.
What I mean is since Akyuu was there and knew the truth, so Keine cannot affect her, because all Keine does is alter history, not truth. Same deal with Yukari and any youkai that lived at the place and time in which Keine is trying to revise the history of.
Certainly arguable a bunch of ways, but in my book global (or at least, Gensokyo-wide) area of effect and seemingly very few drawbacks make up for the techically much more directly powerful effects a lot of other abilities have.
You can't really compare the two, one affects how people perceive history. While fate and miracles have a direct impact on reality.
Of course, how many people in Gensokyo can really prove her wrong? I doubt many people outside of Human Village really keep track of any sort of history. As such, if she changes something about history, there are few people who can really object her.
Sure, no one can object to her. But it is still that, history. If someone were to read the Chronicles of Gensokyo after Keine alters history, her history will get overwritten by Akyuu's history, because that is the last thing they read. And if you want to provide proof to object to her, you could ask for reference and refer to the same Chronicles or some other history book.
It is like having 2 people write different books. Keine writes that Youkai won the war. Akyuu writes that Youkai lost the war. If you read Keine's book, you might believe in Keine's history. If you read Akyuu's book, you might believe in Akyuu's history. Neither of this may be true, it could be possible that the true history was that it was a draw. But that doesn't matter, because as the reader, you do not get this information. All you have to decide upon is which history to read and therefore believe.
@Yuugi's ability: I just take it as she doesn't really have an ability. Since that ability has no real meaning.
@Komachi's distance manipulation: You sort of see it in the fighting games where she swaps you and herself.