It works. Hallelujah.
I went into the URLs section of RCDefaultApp (which is a preference pane), and disabled the following protocols: itms:// (this seems to be the most prevalent in my limited testing), itunes:// and itmss:/
(That issue was particularly grating as I do my web browsing on my iMac but run iTunes on the Mac mini, so I have zero interest in having iTunes load up on my iMac when I’m reading web pages and following unlabeled links from a tech blog. But I can’t uninstall iTunes on the iMac as I need to sync my iPhone’s address book once in a while.)