Sorry, but you are wrong about this. CONSULT scan will provide much more info than CEL scan because it performs diagnostic tests other than just reading stored faults.
I know this because I had intermittent problem with ABS computer which caused multiple faults and warning lights including speedometer failure, all traction control and ABS failure, and other faults. I have OBDLink and performed multiple scans which only reported P0500 fault (vehicle speed sensor). The CONSULT scan revealed faults on multiple systems and low voltage warnings which ultimately pointed to the ABS control unit failing such that it was creating shorts on CAN bus. Resetting system and clearing faults would temporarily work, but problem kept coming back and was only corrected by replacing the ABS control unit This was roughly $1500 item which was replaced under warranty.
My point is that it is not always necessary to pay for CONSULT scan, but CEL scans are sometimes worthless to help you pinpoint problem and every dealer is not trying to rip us off.
For the case reported where dealer found fault which saild OP needed to replace ECU and harness, it indicates to me that there is likely some component in the system which is pulling down the CAN bus. No CEL reader is ever going to pinpoint this, and even the CONSULT scan is likely to give multiple false faults.
I'm a retired semiconductor reliability & failure analysis engineering manager who worked on many automotive ICs, and have experience with this type problem. Bus faults can be very difficult to pinpoint because a component with marginal leakage can can produce intermittent transition faults which are dependent on many factors including the state of the other systems. CONSULT scan may not give the definitive answer either, but will give much more info to point in the right direction. And finally, I would insist that the dealer perform more than one scan - resetting systems and clearing codes in between successive scans in order to check the consistency of findings.
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