Just as a point, Leonidas stands up to thousands of archers, and comes through without a scratch.
300 - We will Blot out the Sun. - YouTube
THIS is what a high level fighters in D&D look like.
20 archers on the walls? Not even a speed bump.
By hiding behind cover, since they know that the arrows are going to do damage to them, if not outright kill them, without it. Sure, they act all cool and badass about it, but they're also not metagaming the fact that the arrows were shot by low-level mooks, or that they have a ton of HP so can take a few arrow hits.
Now have a look at the end battle. Without the cover of shields, the spartans end up going down by 2 or 3 arrows each, fired by mooks.
The thing is, D&D is great for simulating a pitched battle between two sides. Levels give interesting powers and the basic battle modifiers, and the HP to go up against tougher opponents. But then HP break down when presented outside of regular battles. Stuff like falling damage, or when helpless, or wading across a river of lava.
I understand what you're saying. HP's being at the levels they are, or climbing to the levels they do, does seem to be a problem to some. It's not a problem to me, because I don't see Hit Points as purely physical, I see them as an abstract quantification of luck, stamina, ability to avoid or turn damage, fatigue, and yes, a bit of phyisical damage. I'm fine with other people thinking differently. But I don't think Hit Point levels are the core of the problem. I think that, mechanically, fixing the problem with realism (like falling) by reducing Hit Points is a mechanically poor way to do it. I'd much rather want the damage expression of a fall to be changed. Like what Elf Witch was saying. Higher Hip Point loss for falls (more than just 1d10 per 10 foot), and a save vs. death after a certain height (for me, anything above 20").
The issue with HP are that they are applied all the time, despite there being situations where certain aspects of it don't apply. But since a lot of what makes up HP are intangible, and in undefined amounts, it's not really practical to try and pick out which 'bits' of HP apply to each unique circumstance. Nor could a set of rules really implement it in such a way that it satisfies every possible situation. So it might be too much to ask of D&D 5E to codify detailed rules for things like a 'realistic' amount for falling damage, while keeping things in check so that fights with potential falls can still be fun without characters being all but auto-killed if they're pushed off.
As for Archers, I'd fix it by not allowing Dex or Defense bonuses to be part of avoiding an arrow, only armor and shields. In real life, nobody has the ability to "dodge" arrows in real combat. People do put on exhibitions of this, but it's from a specific distance, and constistently practiced at that distance, with the same bow, same arrows, same everything, so that it's just a matter of timing. In real combat, those are variables one can only guess at, and though someone might occasionally get lucky and dodge or bat away an arrow, they are still going to be hit more times than they succeed.
Deflecting arrows may not be something that is possible in real life, I still don't feel it's out of bounds for it to be a possibility in heroic fantasy. I wouldn't want D&D to be distilled down into a real world combat game. One thing I will agree on is that D&D has always been about grand heroics. We're not playing Storm Trooper #5, we're playing characters akin to Luke and Han and Leia, those who have it in them to go beyond the bounds of normal life. The characters who have the will and fortitude to push through nigh-impossible odds to win the day.
There are limits, of course, that are usually defined by the world in which the characters exist. Even in the same world, as this very thread has shown, there are differing POVs and levels of believability that people are willing to accept. Even with a goal of unifying, I doubt that the rules will be so comprehensive as to satisfy everyone, nor do I think they really need to be. 99% of the time, D&D is a fun and enjoyable experience and a great vehicle in which to tell the fantasy stories I enjoy. When 5th comes out, I'm sure I'll end up playing it at some point, and enjoying things, as I've done with all the previous editions, even if the falling damage expression doesn't suit every fall, or it takes 20 arrow shots to finish off a helpless fighter.
At the same time, it would make me happier if there were rules, even optional ones, to cover such situations more to my satisfaction, without having to resort to house rules or DM fiat.