At the risk of pointing out the obvious...
Expertise in a particular subject area does not make someone an expert on
whether a particular topic in that subject area belongs in Wikipedia.
Expertise does not give anyone the right to dictate Wikipedia content.
What it _can_ do is make a person a facile researcher capable of quickly
marshalling evidence on whether a topic meets criteria for inclusion--
criteria that have been established by the _non_-expert Wikipedian community.
If someone were to contribute an article on the Roadshow barbershop quartet,
http://www.roadshowquartet.com/ , it would properly be deleted as not meeting
WP:MUSIC or WP:BIO. The world's greatest expert on barbershop quartets
testifying to their notability in the barbershop community would not matter,
and ignoring his testimony would not constitute bias against expertise.
On the other hand, if someone contributed a scrappy substub on the Buffalo
Bills that failed to mention, say, their Broadway appearance... someone
unfamiliar with them might well nominate the article for deletion.
An expert saying "that's ridiculous, they're notable because I'm an
expert
and I say so and anyone who doesn't agree is an ignoramus" would properly be
ignored.
An expert could, however, quickly point out half-a-dozen ways in which they
do meet WP:MUSIC and my guess such a presentation would garner quick support
the article would be kept--because the expert _used_ his expertise, rather
than _asserting_ it.