I've always found that the people most concerned with someone else's belts are just insecure and afraid that they aren't being appreciated for how bad ass they are.
"This instructor organizing a curriculum by color so he can keep track of people, and students happy they are advancing through it! That's not Muay Thai! They should know they are humble maggots until they win a fight on TV! Only people who have accomplished what either I or my teacher have accomplished (could be anything) have earned the right to rub it in other people's faces."
In real life, people I know who are actually bad asses, don't care about, nor do they have anything to say about, karate belts. They all got their black belts in like 3 years and then kept doing martial arts for a decade or two after that. Worrying about some karate or muay thai teacher giving out pats on the back in public for taking up a new hobby during the first couple of years is beneath them.