Work is being done on this because this is an open source project: no-one is paid to do engineering effort just to please the masses who use copyartifact-plugin. I filed the ticket, I contributed the patch (and then Kohsuke contributed a change to the copying algorithm to make it faster). It's a third party plugin with individual contributors "scratching their own itch" - which is what happened here.
Motivations aside, you didn't respond to my previous request, Ringo:
Would you mind testing the performance of 0.21? It has something that should hopefully be a great performance improvement from 0.20, but still fingerprints. Let us know if you're still seeing unacceptable performance levels. (Preferably with some numbers on before / after performance for 0.19 v 0.21)
And yes, JENKINS-9741 should probably be resolved. I've encountered it myself, but the workaround was trivial enough for me to not care to delve into the root cause. Maybe it's time I did that now.