The Beatles are truly incomparable in terms of fame, but Miles Davis is a global phenomenon as well. He is very well known by pretty much all serious music fans.
Though I suspect you'd conclude that not knowing Davis' discography automatically makes me not a serious music fan.
Not necessarily. Just not a serious jazz fan. Most people when they say they are a "music fan" invariably mean rock/pop of various stripes (from indie to metal and everything in between) and not jazz, or opera or "world music" so maybe it's that you gave a pretty broad statement with no caveats?
This is a debate, not fallacy UNO.