What cost, exactly, do magic-users pay for this? Unless you mean the spell itself, which was a cost to begin with...that is, casting the spell at all requires the resource in the first place. If that counts, why doesn't the Fighter's Action Surge let her deal damage with every attack made using it? (Since I doubt you'd be okay with that, given the way you phrased the cost.)
Yes, the major cost is the spell slot. I don't know that you're reading my post, because the line afterwards is
Me said:
Like, if a 5e fighter wanted to use their Action Surge (forex) to deal half damage on a miss, I'd be generally cool with that.
The reason it DOESN'T is likely because for your Mythical Typical Player, Action Surge is probably more fun - another dice to roll, another chance to crit, a more flexible action to use. There's less assurance there, but there's more dyanmism, more moving parts, more things to interact with, a bigger chance to grab the table spotlight and let everyone else go "woah."
But like I said, mechanically - even with HP-as-mostly-meat - I'd have zero issues with a player who asked, "Can I spend my use of Action Surge to just deal half damage from this attack, even though I missed?" Heck, that might be on the
weak side - I might say "You know what? If you spend action surge, we can just say you hit." (Even that doesn't carry quite the high-level oomph that a big AS does, so I'd probably think it was kind of a bad trade - maybe worth it from a confidence/loss aversion/ "THIS COULD BE THE LAST HIT AND THE BREATH WEAPON IS RECHARGED" standpoint, though.)
I'd typically narrate it as not-actually-a-miss, but as actually grabbing a small piece of them despite
almost missing. That is, it wouldn't just be battering and exhausting and tiring and plot-armor-ing in my HP-is-mostly-meat world, it would actually be a hit, just not a very strong one.
I can get why other tables would from a more "sim-y" perspective based on what attack rolls vs. saving throws represent in the world. I wonder if that group would be cool with damage-on-a-miss if the fighter had some ability that was like "every creature within 5 ft. takes damage as if they had been hit with your weapon. A successful Dexterity save halves the damage." (It's a little Legend of Zelda whirlwind attack, perhaps).
But point being: DoaM futzes with more than just your HP narration.
Given the conversations I've seen from a number of people--not everyone by a long shot, but a very substantial number nonetheless--who feel the "all monsters are just bags of HP" situation really does constrain their ability to play the game the way they wish to...
Well, let's just say that "it's not hard to complexify the game" is not nearly the truism you'd like it to be. I'm not saying it's false, but enough people question it that I couldn't accept it as self-evident even if I wanted to.
If people think monsters are too simple, it's not hard to complexify them - add some spells, give them unique attacks, use action-activated terrain, toss in a mix, use lair actions, etc., etc., etc.
Just because folks think a thing is too simple doesn't mean it's hard to make it more fiddly.
And the simplicity - the straightforward monster mechanics or the easy-to-learn Action Surge mechanics - are appealing to folks who have never hefted a d20 before. One of the big wins of 5e from my casual/newbie group is that it is SIMPLER, that there are FEWER options - they find this leads to more role playing and less fiddling about with things, and more dynamic, fluid gameplay. And this is a group that started with 4e, so it's not like their view is exactly driven by nostalgia bias. They just aren't tactical, optimization-oriented, fiddly players who spend their weekends posting on D&D message boards like I am.
