Ask HN: How does bcachefs compare to btrfs?

The list of features on bcachefs' author's Patreon [0] is quite similar. How does bcachefs manage to do the same in less code?

What are the on-disk mistakes that he means by saying "now [btrfs] has too many design mistakes baked into the on disk format"?

[0] https://www.patreon.com/bcachefs