This is both true and also if followed would fly in the face of what XMPP (and the Mastodon-flavored ActivityPub-powered fediverse of microblogs-and-more) is supposed to be about. And it's also both true and yet people understand what "email" means and how to use it without constantly and consistently running into issues trying to bang out a reply to alice@gmail.example even when the sender's inbox is hosted @yahoo.com—nor do folks spend much time thinking about how and why AT&T's SMSes (for example) are able to make their way to their friend's device even though they use Verizon (to give another example—and if they even know which provider their friend uses at all).
One thing that Jabber (and, later, Mastodon) did wrong was to take the unfortunate stance that it wouldn't be too big of a deal to adopt email-like identifiers without actually being email or implying that Internet-standard email services are available; it was felt that users would just be smart enough to adapt to it. This was a mistake.
The confusion with email, though, can be exploited as useful momentum—something that the network has going for it, instead of a flaw.
If the author and the rest of the Jabber/XMPP community wants the public to "give Jabber/XMPP a shot", then it probably does need (a) a flagship instance (a la mastodon.social) that controls multiple domains (the way that many email providers like Runbox or Fastmail do) and requires the user to pick which one they want their handle to be associated with at signup, in order to introduce email-like decentralization to the userbase as early as possible, and that (b) raises the bar by setting a standard among Jabber/XMPP instances and actually offering email services to that userbase (prior art: Google married (XMPP-based) Gtalk with Gmail in the early days).
While undertaking all of this, an effort to update the XMPP protocol (a la JMAP, but in a backwards-compatible way) while simultaneously reconciling it with legacy email (also in a backwards-compatible way) wouldn't hurt—where "backwards-compatible" here means "to gracefully degrade and provide a fallback" (prior art: Delta Chat).