Maybe btrfs has no fsck,

That was basically FUD. In reiserfsck there's an option to rebuild the filesystem entirely - you're essentially telling it 'this filesystem is trashed; just look through the disk for anything that might be a valid filesystem structure and cobble it together if you can'.

The 'problem' of mistaking a superblock in some image you have somewhere for the start of a new fs is *exactly what you asked it to do*, so those who complained so loudly about it really have nobody to blame but themselves.