Hm yeah not sure but I like the Unix philosophy very much: one tool does one job very well. It sounds like this is one of those situations.
Btw I have a backup server that runs a nighly bash script with all kinds of jobs via ssh on the client machines: dumps, rsyncs, cache stuff, etc. That script then also runs restic on the clients via ssh one by one (ssh from backupserver to client and there restic sftp:backupserver:/…). That way the repo is never still locked and everything is done in an orderly fashion. At the end the whole repo is rsynced to an external location so I could do a disaster recovery.
From time to time (if there is time to spare) I manually run a forget and prune script that does take forever. Works pretty well so far.