I managed a hobby shop for 6 years. Popular is absolutely not a good indication in hobbies. Far too many times someone would stick with a brand/option they knew when there was a product that did what they claimed to want better but required learning something new.
Popularity is a terrible metric for anything other than measuring how popular something is. There's usually a host of other reasons that aren't the same for everyone in that calculation.
Sounds like something a movie critic would say. A lot of movies get panned by critics, yet at the end of the day the only thing that really matters is does the audience enjoy the movie. Sometimes a movie will have a big opening weekend because of expectations but then drops off quickly. But a movie that opens well and keeps going strong? People judge it as a good movie.
Same with games. With 5E, unlike previous editions that sold well at first, there wasn't any initial popularity followed by quick decline. Instead we have year-in-year-out growth. To me, that means people judge it as a good game.
Maybe you like the art-house version of TTRPGs. That's fine. But year in year out growth with no other TTRPG nipping at their heels? You don't get that with a bad game. People continue to buy the game because they have fun playing. I can't think of a better definition of good than that.