I don't think any of that means the benchmarks shouldn't be taken seriously. GP didn't say they expect Bcachefs to perform like EXT4/XFS, they said they expected more like Btrfs or ZFS, to which it has more similar features.
On the the configuration stuff, these benchmarks intentionally only ever use the default configuration – they're not interested in the limits of what's possible with the filesystems, just what they do "out of the box", since that's what the overwhelming majority of users will experience.
Anyone who uses zfs out of the box in a way substitutable with xfs, shouldn't. So I guess they serve a purpose that way. But that argument doesn't need any numbers at all.
> Anyone who uses zfs out of the box in a way substitutable with xfs, shouldn't.
Substitutable how? Like, I'm typing this on a laptop with a single disk with a single zpool, because I want 1. compression, 2. data checksums, 3. to not break (previous experiments with btrfs ended poorly). Obviously I could run xfs, but then I'd miss important features.
On the the configuration stuff, these benchmarks intentionally only ever use the default configuration – they're not interested in the limits of what's possible with the filesystems, just what they do "out of the box", since that's what the overwhelming majority of users will experience.