Agreed on not really a support question. And that to get basic legacy favicon.ico behavior support, no editing is needed and simply placing favicon.ico in the root of the site is something that most browsers will eventually fall back to checking.
If you do want to support more platforms and/or provide richer data to those platforms that support it, then yes you'll need some meta links in the HTML document header.
BoardMagic is great thing for exposing technical options, but as a response to "it should be easier to add favicon data without having to edit overall_header.html", I'm not sure "install an extension and then edit a different event template file" is answering that call for "making it easier."
Didn't phpBB have something like this many moons ago? A section in the ACP where you could paste additional header or footer HTML, independent and outside of any selected style? Maybe I'm remembering some other application.
Anyway, if you do want to make a post over in phpBB Ideas
Or maybe someone knows of some other existing proposal that encompasses this we should vote on instead.