When you criticize something that I think works well, I don't think it's wrong to disagree.
It's wrong to attempt to claim that because it's popular, it's essentially anything but well, popular.
So someone says "5E is flawed in X ways"
and you retort "5E is popular, so your argument is invalid"
Then you're not making any kind of rational or reasonable argument, you're just attempting to stop discussion with an appeal to emotion, essentially. That being the irrational belief that popularity represents anything but popularity. There are more specific arguments where popularity might be used as supporting evidence, but the probative value re: anything but popularity is limited.
Quality re: RPGs is subjective. Period. End of story. This was one of the first answers you received. That fact, and it is a fact, remains. No amount of demanding people provide you a "definition of" or "way to judge" quality is going to miraculously transform the objective fact of popularity into the subjective opinion of quality.
EDIT - I'm surprised no-one has brought music into this yet (ignoring the "Classical is the best!" comment, which I think we should). That's a particularly great example of popularity not equalling quality. Otherwise we have to accept that Daddy Yankee, Ed Sheeran, and Zhao Xian are the greatest musicians who ever lived, and I dunno about you, but I'm not ready to do that yet lol.