That may be so. I'm not trying to change your mind, just tell you what I want and how I see things.
If they have just as many attacks from different angles as 12 crossbowmen, then it should probably be just as hard to defend against.
That makes some monsters, like manticores or hydras, incredibly more powerful than others, like Gorgons or Dragons or Balors, based stricktly on the number of attacks. It's a strage assumption, imho. You can easily defeat a high level titan, becouse it only strikes once, but you are defeated by a low level octopus, becouse it has 8 tentacles.
I'm not sure where you're going with this. I think 12 crossbowmen should be dangerous to an evil wizard, as well as things that don't have the necessary natural defenses. That could apply to giants, manticores, etc. If you want giants to be immune to crossbow bolts, put them in heavy armor and give them a very thick hide. Give manticores a very thick, plated skin. If they don't have that type of skin, then yes, make them vulnerable to crossbow bolts.
I'm trying to point that "thick armor" works for a strict narrow type of monsters. Dragons fill the niche. Other type of monsters, even if they are high level, and supposed to be very powerful, aren't inmune to crossbow fire, so they'll die like flies. In your world, Galadriel is easy as pie to kill by a bunch of goblins with shortbows, but a baby rock troll is not. That makes baby rock trolls threat greater than Galadriel. It does not make sense, in the way the game is developed.
Once again, I'm not trying to say "the game doesn't function this way past a certain level." I'm saying "while I know the game functions this way past a certain level, I'd like an option to avoid that, if possible." That's all. You don't need to prove to me that more powerful warriors exist. I know that. My point is that fantasy is filled with examples where badass people
can be defeated by mundane threats, and that I'd like that type of game to be able to be modeled at all levels. And with the stated goals of 5e, I think that's a fair request. As always, play what you like
My point is that what you call "badass warriors" are, actually, low level warriors fighting in low level adventures, which happen to be very nicely writen. Aragon fights a bunch of orcs, some goblins, a warg or two, and defeat (hardly) a *baby* troll. He scares of the Nazgul using a plot device, which is actually not one of his character abilities, but something the DM gave him to be used there. That's a 5th level adventure in D&D. D&D can, and does, make a wonderful job representing Aragorn. He is a 5th level Fighter/ranger. He dies if he is not careful against a bunch of orc archers. He can defeat, narrowly, a troll. And he will be toasted if he tries to fight a Balrog like Moria's or Dragon like Smaug (unless he is given a Plot device, like a black arrow).
D&D *does* work for this kind of characters. It's just that this kind of characters are not 17th+ level epic heroes. Glorfindel *IS* a 17th+ fighter. He can go toe to toe with a Balrog, and he can defeat a nazgul. He is *not* concerned about a bunch of goblins with bows. 12, or 24. He will kill them all. Probably he won't even need to. Intimidate +20 can do wonders in low level scum. If he choose to kill them, he is probably so fast that he can cover the distance among them faster than the goblins can fire. He can dodge and parry arrows, and he slices through their ranks as a hot knife in butter. There's no chance he loses against 12 goblins. Ever.
Here's the thing, though: just because 12 crossbowmen are a threat to the wizard, it doesn't mean the wizard needs to be impotent against them. Sure, maybe he can kill all of them with one spell. But, if they get the drop on him, ready an action to shoot if he's hostile, and order him to surrender, I want to be able to play the game in such a way where that threat carries some weight mechanically.
That possibility is there in D&D. A 5th level wizard can kill 12 crossbowmen with a 5d6 fireball if he acts first, but he dies if he doesnt. A 20th level wizard is another matter. 12 goblins can't defeat Gandalf. Ever.
However, I think I'll stop the argue here. I don't want to look argumentative. Play as you like, as you say. However, I still think you are mixing things. Playstyle, and level, are different things. D&D can be gritty. It can't be gritty at high levels, because it works with the central idea of characters that grow from killing goblins, to slaying demon lords. Some one who has the chance to survive a demon lord, isn't concerned by a local town guard in a tavern brawl. If you don't like high level adventures, then don't level up. E6 is a great take on this.