The core systems seem strong but with lots of asterisks to keep them backseat to player agency.

I think it’s more that the mechanics take a backseat to the fiction, and largely the GM is more responsible for that than the players. It’s definitely not for everyone. I run a regular 5e game and I suspect half of my players would be into it and half would very clearly say “no thanks”.

lots of pressure valves to reduce the impact of unlucky dice

That’s an interesting interpretation, considering that success with fear is just as likely as failure with hope. I don’t see this as primarily existing to make things easier for the players. Rather it’s there to make each roll more interesting.

Fear seems like it only exists to give the GM permission to do normal GM things

The communication around Fear could be better in the book. GMs can do normal GM things whenever they want. Fear is used to up the stakes by using special adversary moves, taking more “turns” than they can naturally, or interrupting the players in ways that would likely seem unfair in 5e.