I'm going to lead with this.
Oofta. This isn't apples and oranges. This is like petunias to Supermassive Black Holes.
I'm not going to enumerate all the reasons why a tribe paleolithic hunters trapping a herd of RELATIVELY SLOW-MOVING...NOT FLYING...NOT COLLOSAL...NOT GOD-LIKE OMIDIRECTIONAL ATHELTICISM-ENDOWED mastodon in a kill box and MAYBE slaying one with an onslaught of spears from range is NOTHING LIKE a singular warrior wading into melee and clashing with an Ancient Wyrm.
Come on man.
Or...you can do the D&D thing and compare the Mastodon's stats/metrics to that of an Ancient Wyrm! The results won't be pretty (for your attempted refutation)!
So, to be clear, I didn't mean what I wrote above as an opinion. I meant it as a truism. Because its true.
* It is true that the morphological and biomechanical traits of dragons (particularly the larger variety and especially Ancient Wyrms) would be an impossibility in anything approaching a system governed by anything approaching earth-like parameters.
* It is true that if the above were possible, that mundane humans (even those at the absolute tail of the distribution when it comes to athleticism, mental processing, proprioception, courage) couldn't dream of even withstanding a singular moment of melee clashing with these colossal, endowed-with-impossible athleticism creatures.
These two things are fundamentally true.
What isn't true is what you have both written above.
There is no evidence in any of D&D that Dragon morphology, ability to respirate, biomechanics, athletic prowess, or flight are supernatural. I'm looking at AD&D 1e MM. Nope. I'm looking at B/X. Nope. I'm looking at RC. Nope. I'm looking at 3.x. Nope. 3.x tries to bin a whole lot of stuff under the sense-defying, total-hack Simulation patch, Extraordinary (not magical but may break the laws of physics...whatever the hell that means!) keyword...again...a complete patch for historical game problems (one that wasn't carried forward).
There is no precedent that I've ever heard in D&D of a dragon being unable to move, fly, claw/bite/tail swipe within an Anti-magic field or when Dispel Magic is placed upon them. If this is happening in D&D-land I would love to hear about it. Tell us about the stories of the Wizards in your games curb-stomping dragons with a nicely timed dispel when the dragon is flying! CRASH. Ok, now they can't move or claw/bite/tail because their biomechanics are shut down so just enstabinate them until dead. My guess is this hasn't happened in your games (nor anyone else's games). If it has, I would love to hear about it!
Dragons HAVE magic. Their morphology and biomechanics are not magic.
And ok...let us use the sense-defying 3.x Extraordinary keyword for dragon morphology and biomechanics. Why wouldn't it be a prerequisite for epic heroes to ALSO have their morphology and biomechanics fall under this exact same Extraordinary keyword? There we go! Simulation satisfied. Epic Warriors can now wade into melee and clash with dragon because their athleticism breaks the laws of physics without being magical! I expect a slew of D&D posts about this now and I expect a cavalcade of play excerpts regaling us all of your 18th level Fighters doing 30 ft standing Broad Jumps and 15 ft standing Vertical Jumps and cleaving mountains and holding their breath for 2 hours! My guess is this hasn't happened in your games nor will it ever happen. If it has, I would love to hear about it!
And it all comes back to things like HP, To-Hit, Armor Class, and the keyword "Wounds" for the Cure Line of spells. The worse part about HP is that they actually model physical and mental resolve/stamina BEAUTIFULLY. If your gas tank is waning YOU KNOW IT and you know that every clash/effort (whether you're in a grapple, sparing, or climbing or trying to defend someone on the basketball course/hockey rink) at that point might be your last (before you fail at the endeavor/lose the matchup). That is the exact internal causality model of D&D and the exact cognitive state inhabited by PCs etc
If folks didn't interpret “to hit” (in melee only...not other target numbers) early on as “creature in imagined space” rather than “target number" and we had the nonsensically nameed Cure Wounds line changed to Restore Vitality....well D&D would have historically worked infinitely better as both a Game and a Simulation and we wouldn't have had these ridiculous culture wars around D&D as Simulation and HP as meat.
Finally, ironically a game like Stonetop (not remotely a Sim game) is infinitely a better Sim than D&D when it comes to this stuff. You have a HP pool that doesn't grow and it measures your physical/emotional resolve/stamina etc. You have Armor as "Soak." You have the Weakened, Dazed, Miserable Debilities that actually negatively impact your performance in ways that hews to those conditions. You get actual Injuries that shut down possible moves in the imagined space or hinder you dynamically. You have a recovery model for these things that is infinitely more sensical than D&D!