Just want to say that "ooooOOOO, infinite universessss" is and always has been a totally stupid plot point. It makes everything you could say about your fiction completely irrelevant, because all of it is not only not special, but guaranteed to happen, as that is what happens with the concept of infinity.
Yes, of course Comstock is actually Booker. There's also a universe where the exact same thing happens, but the only difference for that entire world is that Comstock is wearing a red baseball cap. There's also a universe where Comstock is Booker's son, Booker is Comstock's nephew, Booker is Comstock's third-cousin from the other side of the galaxy and is actually a tentacle monster, and so on forever and ever.
It doesn't matter if I save Elizabeth, because if I didn't, she was saved in another version. Or if I did, she wasn't somewhere else. Everything you can imagine not only can happen, but does. And not only does everything happen once, it happens an infinite number of times.
That idea doesn't blow my mind; it breaks my heart. Hard to care when, in an attempt to be clever, you're essentially saying "nothing matters."