Annex isn't slow because it's written in Haskell, it tends to be slow because of I/O and paranoia that's warranted as the default behavior in a distributed backup tool.
E.g. if you drop something it'll by default check the remotes it has access to for that content in real time, it can be many orders of magnitude faster to use --fast etc., to (somewhat unsafely) skip all that and trust whatever metadata you have a local copy of.
E.g. if you drop something it'll by default check the remotes it has access to for that content in real time, it can be many orders of magnitude faster to use --fast etc., to (somewhat unsafely) skip all that and trust whatever metadata you have a local copy of.