I get you, but I feel like the closing minute of Episode 8 - where Billy looked around his room and realized it was all him - basically revealed all of that. Episode 9 was just elaborating/deepening that, along with Billy wrestling with the implications.
No, the revelation at the end of episode 8 was just the beginning. It established
what happened, but episode 9 explained
why, which is even more important. At the end of episode 8, we knew nothing about Nicholas Scratch, nothing about how the idea of the Road came about and what it was really for, none of that. The end of episode 8 was just the end of the setup. Episode 9 was the payoff, both narratively and emotionally.
Little aside, but while I have no issues with diversity in casting, I kept wondering where in 1750 colonial America this was that there were roughly equal numbers of free black and white peasants living without social segregation. This stuff doesn't bother me in fantasy settings and such, but when something is supposed to be a historic setting, I don't like antiracism-washing when we make segregated parts of real history seem contemporary.
The groups we saw here were apparently "witch" communities, so these would have been marginalized people to begin with, coming together to build their own communities outside the mainstream. It makes perfect sense, then, that they would have been diverse, that they would have welcomed escaped slaves as well as persecuted women, gay people, etc.
Also, while I understand Agatha's magic-absorbing/witch killing powers, I feel like the whole quick-cut aspect of the flashback just made her seem like a witch serial killer. I am under the impression she only needed to do that when her magic was depleted. It's not like we saw her doing much with it while she wandered the woods with her son. Why did she keep hunting down covens and killing them? I feel like this could have been made a bit cleaner if it didn't seem to imply it happened so frequently.
Well, yeah, that's the idea. Agatha is a villain. Sure, she loved her kid, but so did Thanos.
Didn't her detective delusion in the first episode entail hunting a serial killer? Maybe that was a clue to her true nature. Another clue was the rumor that she was the only person ever to have come back alive from the Witches' Road. Now we know where that rumor came from -- another reason the final episode was the payoff, not just the epilogue. It's not an epilogue when the detective explains how and why the murder happened and exposes the characters' hidden secrets, it's the climax. Everything in the previous episodes was a clue to the mystery that was explained in the finale.
And Agatha would've gotten away with it too, if not for that meddling kid...