Worthless? Maybe not, but it's probably not going to carry a lot of weight if they have no experience outside of one or two editions of a single game.
Like, imagine the following examples.
1: Anime
"Sword Art Online is one of the greatest fantasy anime shows ever made."
"Er...what makes you say that? Because it's pretty controversial, and plenty of anime is way more fantastical, both before and after it."
"Well Sword Art Online and .hack//SIGN are the only two anime I've ever watched."
"Wait so like...you've never seen Frieren? Or like Inu Yasha? Or Fullmetal Alchemist: Brotherhood? Hunter x Hunter? Anything from Studio Ghibli???"
"Nope."
2: Cuisine
"Traditional Cantonese sweet and sour pork is one of the greatest dishes ever to come out of China."
"Really? That's pretty basic, have you ever had char kway teow or char siu bao?"
"Never heard of 'em."
"Wait, really?"
"Nope. The only traditional Chinese dishes I've ever had are sweet and sour pork and lo mein, and sweet and sour pork is way better."
3: Novels
"Harry Potter is the best 'young magic user' series ever written."
"Really? Even with all the controversy from Rowling?"
"I mean, I wish she wouldn't spout off about politics..."
"Oh, no I meant how it's super derivative of Ursula K. Le Guin's Wizard of Earthsea books."
"Never heard of 'em."
"Wait, what?"
"Harry Potter and The Wheel of Time are the only fantasy series I've ever read. Well, I only read the first three WoT books, they got too boring to continue."
No one can tell the first speaker in any of these things are things they shouldn't like, because that would be telling them that their preferences are wrong. However, people absolutely can question how much merit, if any, there might be in these sweeping claims about the prominence of some particular thing amongst a field of things they don't actually know anything about.
When the one and only thing you know comes from a single source, out of many, many other sources, it's quite easy to lack context or nuance. Just as someone doing history research prefers to have as many sources (and preferably as many primary sources) as possible, in order to avoid risk of any one source being distorted or biased, someone talking about "simulation" in gaming is....gonna really want to have played at least a few different games that do sim, or at least to have read them even without playing (though play is vastly preferable).
Pure preferences cannot be argued about. De gustibus non disputandum est. But claims about the efficacy or prominence or functionality of something are not merely preference. They're a description of where that thing fits into the broader context. A person making such statements who doesn't actually know that broader context isn't saying very much.
And, unfortunately, it is very very often the case that people who play D&D have never played any other game. Hard to draw any contrast or speak to the effectiveness of D&D when you know nothing about the alternatives, even within a narrow range like "games that place special focus on sim".
So because I don't play a dozen different games I can't have a valid opinion. Even if I've read up on, read through countless posts, watched live streams? If I don't have the chance or opportunity to play other games, isn't it on you to explain the difference? Could it be your fault that your explanations aren't good enough?
Because to me it sounds like "I disagree so your opinion is invalid".