Threads in the original discussion page are often sorted by the first post of each thread. It might be preferable to preserve (or try to preserve) that in archives. It can be necessary to insert threads into somewhere in the middle of an archive to do that, instead of simply appending.
It would be nice if this is configurable by a parameter in the config template. For compatibility, the default behavior should fall back to no sorting (just appending).
Also, when you sort by the first post, I think it makes sense to use the same criterion for selecting time-based archives. For example, threads created in 2020 should go to /2020. (If including this makes the task too large, please feel free to leave it out for later.)