Why do Chrome and Safari incorrectly render <rb> and <rt> in <ruby> tags?

MDN says that rb and <rt> tags (which are used inside <ruby> tags and most commonly used for East Asian languages) are supported in Chrome and Safari. However, MDN's example renders incorrectly in both. The following is the first example in the <rb> docs:

<ruby>
  <rb>漢<rb>字
  <rp>(</rp><rt>kan<rt>ji<rp>)</rp>
</ruby>

Firefox 78.0.2 ✅

Chrome 84.0.4147.105 ❌

Safari 13.1.2 ❌

Questions

Is MDN just wrong here about Safari/Chrome support?

Or is the MDN example HTML snippet incorrect? (Chrome and Safari both incorrectly render various examples in this 2015 Mozilla Hacks blog post, "Ruby support in Firefox Developer Edition 38".)

Note that <ruby> tags using just <rt> inside, and without <rb>, seem to render fine in both Chrome and Safari. The second example in the <rb> MDN docs follows, and looks like the Firefox screenshot above in both other browsers:

<ruby>
  漢 <rp>(</rp><rt>Kan</rt><rp>)</rp>
  字 <rp>(</rp><rt>ji</rt><rp>)</rp>
</ruby>

In the comments section of the 2015 Mozilla blog post above, the author mentions that <rb> is not supported by other browsers, could this still be true (despite MDN browser compatibility data)?