When was involved in tennis I was a USTA verifier. The job was to rate a player from 1 to 7 (usually 2.5 to 5+).
When training to be a verifier we watched dozens of marchers over several hours. The players on the court had years playing in adult leagues, and had a consistently solid rating.
After a few hours we all met and compared our ratings. On most courts most verifiers had person "A" as higher than person "B," mentioning footwork, serve, winners vs errors, etc.
A fair amount of the time I was asked why I disagreed, and how I came up with my rating.
"I kept track of the score, and recorded who won and who lost."
My ratings were damn close to a perfect match to each player's rating based on a computer analysis of the several dozen matched they had played.
Ultimately the bottom line is the bottom line. I don't think Clingan has been given enough minutes to draw the same conclusions you state above.