I have my doubts about that situation. But yeah, you're basically right about it being the market for appraisal services which effectively determines how much or how little development and reporting is sufficient for their usage. (aka "meaningful" to their intended use) Not the appraisers.
According to the GSEs and almost all Lenders, this is "meaningful" to their intended use.
From Fannie Mae:
Fannie Mae Guidelines require Sales Comparison adjustments to be "
Market Derived," including the Sales and Financing Concessions adjustments.
From a Big Box Lenders 21 page engagement letter:
Not to mention USPAP requires
"evidence and logic."
If you think the majority of secondary market appraisal adjustments are market-derived well, you live in a dream world.
What happens is the appraiser who goes through the process to comply with these guidelines, i.e., mandates, are punished, and the ones who flaunt them get rewarded.