I also find these conversations frustrating. I'm trying to say 'please actually read the rules for these games, and you will see they are not the same thing', and I get responses that make it sound like I'm trying to be the Chief of D&D Club Membership.
So, let us look at that a bit.
You ask folks to "actually read the rules" - we will set aside the possible condescension of that suggestion for the moment - "and you will see they are not the same thing."
Well, of course they aren't
exactly the same thing. That's trivial. But we then get to how
meaningful the differences are, and upon which differences your argument rests and what you are asserting about those differences.
So, if you are saying, "X and Y are different in <this specific way>, and that is terribly meaningful and it means <specific thing about play>..." and folks disagree with your assessment, you will get pushback. Those asserted meanings often look a lot like gatekeeping, asserting a right and a wrong way to play - which is typically coincidentally aligned to the speaker's own preferences.
To which the collected answer is usually of the form, "For crying out loud, stop telling people how to have their own fun already!
I ask people to explain what they think D&D actually is, in a positive sense, and no-one can explain, except to say that it's unique and ineffable and I will never find a satisfying answer.
Well, yes, that'll happen when you try to nail people down to defining it as one single thing, when... it isn't one single thing in application.
D&D is a set of rules that can be applied to play an RPG. Those rules are not explicitly proscriptive about what kind of game it can be, or what the goals or style of play will be. As a practical matter we can allow that those rules are better at supporting some styles than others. But, folks have a good time using them over a wide range of playstyles.
Right now, I'm playing in one game that's very dungeon-crawley, combat-on-a-map every session, where most problems are solved by deadly force of arms, and a few are solved by the party Paladin rolling a natural 20 on a persuasion check, much to the party bard's chagrin.
Meanwhile, in a game I am running, the party is almost level 4, and the only things they have killed are two goblins and a gelatinous cube.
Both are very obviously D&D to anyone observing. But they aren't really the same either. Players are having a fine time in both.
Do not confuse "ineffable" with "flexible".