There's a lot going on in the OP that's tangled up. For example, I don't even know what the arrow catching is doing in there. D&D characters can do all sorts of unrealistic and fantastical things. That's kind of the point.
I don't think this "real people are tougher than you think" point really goes anywhere. The examples just shift the conversation up a few character levels. Let's posit that humans can survive a spear wound. How about 5? How about 10? How about 50? Even when you import a "realistic" sense of what people can do, D&D characters are going to far outstrip it, and it won't take epic levels to do so.
So, what argument is left?
To answer the question in the thread title, mostly, I think SolEiji is right about SKR problem. As a descriptive matter, I think that's largely true. And, it gets further magnified by the fact that we're not even talking about "real" people here, but action hero types. We're talking about Conan, not Sir Richard Burton. So, their capabilities are being doubly discounted.
I think there might be a subtle, but not terrible argument to be made about the difference between inhuman skill/reflexes and hit points. It goes something like this. Catching arrows, the godlike speed of hinten mitsurugi, or some other superlative skill is a defining feature of the character. It's the "thing" the character can do. Large numbers of hit points, and their wonky relationship with real world examples of harm (e.g., a spear thrust from an ordinary bloke) are ubiquitous, though. No one should bat an eyelash at Huma, He of the Iron Skin who is inhumanly tough. That's his schtick. But, it's weirder when Bob the Bookworm can also take what seems like massive amount of punishment -- in a real world sense of X number of sear thrusts -- without batting an eyelash.
None of this really bothers me b/c the game is full of wonky abstractions and is also not there to emulate reality. It's instead supposed to create a cinematic reality. One in which an important named character -- like a 10th level PC -- can't be easily laid low by a lucky soldier. That's patently unrealistic, as Hobbes famously pointed out, but it's needed to emulate the fiction that D&D is aiming for.