Yeah, importing is always better than just copying.
However... Don't bother. The other wiki is big and established, and (probably) has the better url, a community, and better SEO as your wiki gets punished for duplicate content. Meanwhile, you've got to run the wiki by yourself, hoping you fool hapless visitors into thinking you're the prime wiki on the topic. It requires time, dedication and determination, all wasted because they'll probably call Staff on you anyway. All that out of spite is a fool's errand.
You think you're in the right. But maybe you just don't know something. If it seems obvious to you but isn't there, maybe it isn't there for a reason? And maybe the admin sounds short and robotic because they have to revert that every week?