That's unfortunate. After looking into your comment, I see that another post has discussed making chunker more context-aware, although the idea seems to be too much work to implement (here).
Despite this, I would still like to keep the mv operations from hanging for so long and either have them work faster or act asynchronously (So if you happen to know a way to do this, let me know!). I did test some proof-of-concept changes and it seems that server-side copies are in fact faster when made parallel. The slow server-side copy does indeed affect non-chunker and chunker backends on larger files, but chunker has the possibility to improve this by working on multiple chunks in parallel. I still think this may be something to potentially consider for a feature given the difference in timings.
Before proof-of-concept:
localhost:/var/opt/test# time mv Archive.7z Archive-1.7z
real 1m 18.14s
user 0m 0.00s
sys 0m 0.00s
After proof-of-concept:
localhost:/var/opt/test# time mv Archive-1.7z Archive.7z
real 0m 14.82s
user 0m 0.00s
sys 0m 0.00s