That seems off. Wyvern is not even huge. It is large. It is smaller than an elephant by far.Ok, let's nip this in the bud shall we?
A 40 foot crocodile would weight in at 18000 pounds (just as a quick Google Search, I'm sure there's quibble room here). Now, I'm going to put a lone armored man in an arena with a sword and shield and then plunk down Mr. Crocodile.
Who do you put money on? Even if that man somehow managed to kill the crocodile, he'd most likely be maimed forever. Loss of limb(s) at a minimum. Now, a 40 foot crocodile is about the size of a wyvern. Not a full dragon, just a wyvern. A fairly dangerous mid range monster that the PC's routinely kill.
Dragons vary in size, but they tend not even be of the size of largest sauropods. And of course single characters usually don't kill them, groups of people equipped with state of the art (often magical) gear do. And, sure, doing so is an amazing heroic feat, and it seems pretty unlikely. But it doesn't seem impossible to me. It seems like a thing that could happen.The idea that you could routinely kill 9 ton flying crocodiles with a sword without any sort of magic or fantastic elements is a bad joke. Never minding an actual dragon.
And, even if our knight DID manage to kill that dragon with a sword, let's see him or her do it again. And do it a third time. Because, well, in a high level campaign, facing three dragons isn't unheard of. Or, even better, two at a time - something that does happen in 1e modules. There are encounters with multiple dragons in high level 1e modules (and not just Dragonlance). And the party is meant to win these encounters.
Dragons absolutely ARE super resilient compared to real world animals. An ancient red dragon clocks in at around 60 TONS. That's TWELVE mastadons in size, for comparison. Does your fighter kill 12 mastodons with a sword?