Even it was true that there are lots of high volume lenders doing that (citation needed) it doesn't alter the point that nothing that occurs at an AMC is happening without the direct knowledge, endorsement and enablement and even pressure by the lender who chose to go that way; and those lenders have no incentive to do otherwise.
If there really were a lot of high volume clients doing that then it wouldn't have taken you 5 years to recover to the 80% mark of what you used to do. Even now, you admit to having to accept AMC assignments. By my count your own experience obviously contradicts your talking point (a significant number of high volume clients do direct engagement). Not to mention what the other appraisers have been saying about that for all these years. Sorry, but I am disinclined to ignore what everyone else has been saying all along.