Have you ever actually heard anyone mention the application of anti-fungals to citrus fruit rinds in the first place? Because I've never even heard of it outside of mycology circles, and there are virtually no Google results despite the fact that the practice is ubiquitous.
How does "There is virtually no evidence that this is even done" translate to "This is a big problem"? At least in my book, lack of evidence doesn't count as evidence.
Actually a Google Scholar search for 'citrus postharvest antifungal treatments' does show that this is in fact the standard operating procedure. E.g. this paper starts out with a summary of the current state of conventional agriculture:
