There are lots of physically powerful, albeit villainous, casters in S&S, so I'm not sure about this Real Men Don't Use Magic trope.
The "albeit villainous" part here is important.
We're not arguing there's anything wrong with the D&D spellcasting rules. Not in general, and not for use in your S&S games.
We are arguing however, they are not appropriate for
player characters.
D&D magic is too clean, too functional. It works like a tool. It's reliable. There are no downsides.
For a villainous caster who has already sold her soul to dark powers, that's alright. The cost is presumed to already be paid (if nothing else by the fact she's "villainous"). There's no point in keeping records of exactly how far she's fallen. She's an evil NPC and that's enough.
But
for a player character, we must rewind to before the falling-into-depravity part. Back when the cost was something you want to avoid paying. For a player character in a S&S setting magic needs to be at least one of the following things:
* unreliable
And I don't just simply mean a chance of failing to cast the spell (the gun jamming). I mean a risk of the magic hitting the wrong target, or having the wrong effect altogether. I'm talking things like it starts to rain dead frogs after your spell is cast.
* feared and distrusted
And I don't mean the natural fear of getting zapped. A man might fear a sword being used against him, but swords aren't feared and distrusted by themselves.
* corrupting you mind, body and/or soul
And to be honest, preferably all of them. But D&D magic is none of them.
There is no cost to using magic in D&D. While this is essential to supporting the standard trope of "fighter, rogue, wizard, cleric" that's completely antithetical to the Sword & Sorcery genre.