[pm215]

I put my question to a friend of mine who works on linkers, and his take was that for a single threaded linker like ld.bfd the copy-bytes part would probably dominate, but that for a multithreaded linker like lld that part trivially parallelizes and so the slow part tends to be elsewhere. He also pointed me at a recent blogpost by the lld maintainer on this topic: https://maskray.me/blog/2021-12-19-why-isnt-ld.lld-faster which I should go and read...