The author believes that institutional authority and intellectual authority are distinct, but the musicology example illustrates the critics’ claim that intellectual authority depends on institutional authority.

We don’t know whether the musicology example “prevailed in its own time.” Regardless, its purpose is not to describe an argument possessing intellectual authority. Instead, its purpose is to suggest that even when something seems like it has intellectual authority, that authority actually comes from institutional consensus.

The illustration describes a musician who was never found to be a musical genius, not one who lost the ascription of musical genius over time. But more importantly, musicology is an example that the author uses to illustrate the critics’ claim. He doesn’t use it to draw any conclusions about musical geniuses. Its purpose is to illustrate the claim that intellectual authority depends on institutional authority.

The musicology example illustrates the critics’ claim, not the author’s own perspective. He brings up musicology in P3 to illustrate the critics’ claim that determining intellectual authority actually requires appealing to institutional authority. If a musicologist decides that someone is not a genius because their work wasn’t recognized for several decades, this judgement is based on institutional convention, not intellectual authority.

Musicology is just an example that the author uses to illustrate the critics’ claim. He doesn’t use it to draw any conclusions about musicology or the arbiters of musical genius. Its purpose is to illustrate the claim that intellectual authority depends on institutional authority.