* - not a perfect analogy, but I'm hard-pressed to think of good off the shelf tools for what they're looking for. I guess reiserfsck's infamously side-effect laden --rebuild-tree would probably be closest...
(I am acquainted with zdb -r and import -T; neither helps you if there's not enough metadata consistent to get enough of a pool structure in memory to 'import', but one could still conceivably salvage some data in that case.)
The point of those is that the only time a pool is truly unusable is when you can't even import it.
The issue is, I think, people are expressing a desire for a tool that can still salvage data even when you've gone through all the (128/N) -T options and found them all unhelpful.
For more on this, see https://utcc.utoronto.ca/~cks/space/blog/solaris/ZFSScrubLim...
(The tl;dr is that a fsck on an ordinary filesystem has to walk the directory tree to find everything. However, ZFS maintains a separate list of active inodes and a scrub can just walk over them and check the checksums of all of their data blocks. It doesn't have to, for example, read a directory's contents to find further files to scrub.)