Phil,
The Matrix system is only used in Florida with regattas on the national schedule postings. It was found that a true and fair Matrix was difficult to achieve if not impossible. This is in consideration that a regatta has to stop at a certain point where all competitors have completed the rotation needed for all to meet all the same number of times. This is often interfered with by cancellations in the last few days if not the morning of the event.
My experience in sailing all the Florida events a few years ago where the Matrix was the majority used, was frustrating because when the scoring identified the competitor I needed to best I could not get a heat with him in it. Regardless of efforts by the RC this was the case more than not and hence steered the course of the regatta along a path maybe not intended.
Florida has always favored this system for the reasons you state. I have never thought this reason enough where there is no control to the number of competitors on Saturday morning or possible mistakes in the subjection selection process in creating the heat pairings. Ultimately, the fairness of the Matrix is rooted here.
The other consideration that is not mentioned is that while less physical effort is needed a true competitor hates to sail two to three consecutive heats where tweaking is rushed or not available. Additionally, major competitors who attend a Matrix formatted regatta consider it for other reasons and hope for the luck of the draw.
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