The title is weird. The author didn't fight DMCA in SE. He sent an email that was not a DMCA takedown request to a DMCA report address and SE did a nice thing by responding.
I like that SE refused to reassign author - it's not a good solution and they'd end up with two annoyed parties instead. SE did more than they had to here.
Why: DMCA takedown request is a very specific process and it requests immediate removal of content. Poster can then dispute it to get it restored. (http://brainz.org/dmca-takedown-101/) As far as I understand your post, that's not what you submitted since modifying the content / replacing the author is not one of the DMCA outcomes.
Possible: "Asking SE to reown/remove plagiarised content"
Why reowning is a bad idea? Because you didn't create that post and the post has effects inside of SE system (reputation, comment addressing, etc.). Nothing of course stops you from requesting a takedown and posting the same content again from your own account. Request to reown some already posted content seems a bit dodgy to me.
I like that SE refused to reassign author - it's not a good solution and they'd end up with two annoyed parties instead. SE did more than they had to here.