Its clear your "admin" feels threatened. He can't hack it, and he knows his days are numbered. He isn't competitive in his skill level, so he's desperately trying to "defend" his job.
You did the right thing by going around / over him.
Hopefully, you can sell yourself into the soon-to-be vacant position.

If you're already performing the duties of system admin., then I say you deserve the title and commensurate salary.