therefore said hardware doesn't belong on a site that is supposed to be documenting Amiga specific hardware.
Sure, but you could argue that custom machines that are specifically built for AO4 may belong in their own section on the site, because they're Amiga related (while not being actual Amigas). Obviously, macs and pcs don't belong there at all.
but my definition of Amiga is broader.
Your definition of Amiga is irrelevant, because the makers of the original Amiga computers got to decide what an Amiga is, not you. The last Amigas are therefore the AGA Amigas. What you, me, or anyone else thinks, is entirely irrelevant.