I don't think that it poses an issue with merge conflicts. It is likely not an issue as long as the tagging is only made on the main branch by the release managers.
I know it is working well for Linux kernel hackers. Linus does all the tagging, and I don't recall issues with merge conflicts on the top Makefile with the part that holds the version.
I think you're assuming that all software results in a single "release manager".
In many environments, multiple branches of software are deployed and maintained at the same time.
Even your example with Linux; I don't think that is correct -- Linus doesn't tag the stable branches, and others. There is a centralised agreement of how the version numbers are maintained though.
My example is relevant to tagging in branches that may merge back into the main one. The stable branches in Linux are cherry-pick branches that don't get merged back and therefore creating tags there is harmless.
I know it is working well for Linux kernel hackers. Linus does all the tagging, and I don't recall issues with merge conflicts on the top Makefile with the part that holds the version.