No. This is just as incorrect as the OP's point that people are trying to rebut. (And I don't mean to single you out, because a LOT of people are making the same exact mistake, although
@Willie the Duck had a very good post while I was writing this).
Objective and subjective actually have ... meanings. And there is almost NOTHING that we discuss and argue about on these boards that is objectively measured. Depending on how you describe "popularity" (such as "sales in the last year" or "most people currently playing") you could be discussing popularity using objective metrics. Quality, on the other hand, is subjective unless you define it very narrowly ("Tesla cars have had the highest percentage of vehicles sold subject to serious recalls as defined by the United States government during the time period in question.")
This continues to be a source of frustration because we see the same argumentative loop occur. Now, these words can have different meanings in context (for example, "The judge struggled to be objective.") But when it comes to these types of qualities, it's pretty simple-
"Objective" can be measured using an outside referent that is agreed upon. "The temperature right now is 89 degrees." "This year, the company made more in revenue than last year." "That book is 30 pages longer than the other book." "That burger has 300 more calories than the other burger, and 10 more grams of fat." "This car has better gas mileage than the other car." "That SUV has more cup holders than the Ferrari." In short, comparisons that rely on agreed-upon outside facts.
"Subjective" doesn't. It's everything else.
Which is why two things keep occurring-
1. There really shouldn't be any debate about things that are "objective." The burger either has 300 more calories, or it doesn't. While there might be an error in measuring, once the measurement is established there is no real point in arguing about it.
2. Instead, all the arguments are about subjective ...
qualities ... and/or the implications of those objective facts. But because people feel the need to assert that they are right, we continually see the jujitsu of people asserting that subjective qualities (like ... quality, or design, or how "good" something is) is not subjective, but is objective. Because if it's objective, then they can argue that they are objectively right (they're not).
Here, we see this repeat. Let's assume that the use of popular refers to the objective measures of "most people currently playing" and "most books sold" and "most revenue by a TTRPG game." By those three metrics, 5e is the most popular TTRPG game. I don't think that's really in dispute (in other words, I don't think most people would disagree that this is a fair inference to make from those facts).
That said, there is no objective measure for something being "good," or "well-designed," or "high quality," as those are subjective qualities. That's where the OP fails.
What I do think is correct is what I often say- popularity (high sales, dominating the market, etc.) is something that people should pay attention to. Because whether or not it's "good" or "bad" it does usually mean that there is some quality that it has that is appealing to large numbers of people.
Essentially, this leads to frustration to people who don't prefer what is popular, and prefer other things. I prefer a manual transmission in a car- for many reasons, that isn't popular as a giant SUV or pickup truck with an automatic and a lot of cupholders. There are people that prefer free jazz to Harry Styles. I have never watched a single episode of NCIS, but not only is it the top rated TV show ... I just looked at the highest-rated scripted shows on broadcast TV and realized I have never seen
a single episode of any of the top 20 for 2021-22.
Some things that are really popular just aren't for me. And that's okay. But I also realize that people who are making things that are popular are designing things to appeal to people ...
that aren't me. And instead of simply griping that the design is bad, I do make the attempt to understand why that design works for others, even if it's not something I prefer.
Which comes back around to 5e. The most common argument is not some anti-intellectual "It's popular, therefore it's good." Far more often we see people refuse to see that the things that they don't like might be contributors to the popularity of the product; in other words, they might hate all the cupholders or the pop stylings of Harry Styles, but other people seem to like them.
(As always, IMO, YMMV)