I don't believe that any of us assert that Waivers will always run high.
However, a segment of them will, and unlike an appraisal, there is no report that can be forensically reviewed later to ferret out what went bad.
And since the WAIVER status is not revealed out front and is easily accessible for data comparisons, such as the way FHA, cash, etc, are disclosed, it is very difficult to make the comparisons. That means for anybody who wants to study the data, not just appraisers. As for appraisers, having to make multiple calls and emails to brokers just to find out if a WAIVER was used on any one of ten sales is not practical. Brokers and agents have little incentive to return these calls in a timely manner and they may not know if a waiver was granted since, again, there is no disclosure.
I suppose they want it that way. A waiver, after all, is part of conventional lending ( reported as conventional on MLS). I assume the loans granted with WAIVERs are mixed in with the other loans an investment buys, the way perhaps C and D paper was mixed with B and C paper in what they used to call toxic loans,
A segment of high /inflated sale prices influences the market because all that is needed is one high sale price every few months to form a high range of value in the next AVM or appraisal. And while an appraisal can set a poorly supported high value too, at least there is an appraisers name next t it and the lender had to do a buyback if the collateral value was flowed - that is not the case in a WAIVER where the bailout is 100% on the tax payer.
The other difference is once Fannie or freddie greenlights it from their AVM, the Waiver ALWAYS is the sale contract price - unlike an appraisal, which can come in ":low" sometimes.