Anyways, I don't really get the complaint at all.
I'll try and explain my points better. What I'll do is make each of my complaints a response to part of your quote.
Obviously, if you make mages better against plate armored guys than sword fighters, then you need to make sword fighters better against somebody else. Since we're talking about simulationist aspects, you can pretty much make the mage good against whatever you feel balances out the classes with real-world skillsets
Complaint Number 1 - A plausible ruleset screws up the balance of the game. I agree with your point that if mages are better against armoured opponents, than sword fighters need to be better at something else. But is this really plausible (remember we’re trying to create a 'plausible simulation', welcome to the first reason why it would suck.) You can’t just ‘make’ sword wielders better against a different class of opponent when such a scenario is improbable. You also can't apply a plausible ruleset ONLY to the characters with real world skillsets, it should apply to everyone or there's no point. Realistically, mages should easily be able to deal with armoured foe or unarmoured foe alike. Casting a basic fireball which explodes on impact will incinerate a man (this is a plausible scenario) not detract 20 points from their health (this is not plausible.) If a foe is resistant to magic, you apply indirect magic. You crumble the ground beneath their feet, you drop a boulder on them. It would be utterly unbalanced, mages would kick a melee fighters arse in every way.
Games like Baldur’s Gate get around this in many ways. They a) unrealistically nerf magic users and their spells, b) they make armour effectively useless, and c) they use a hit-point system etc etc. All these options wouldn’t be available in a plausible ruleset.
I suppose there are realistic ways to limit mages, like only a few spells a day, but essentially mages are people who can operate outside the laws of physics, so they’re always going to have an advantage. This is why fantasy authors have so much trouble trying to create a gritty magic system.
haven't RPG rules had certain weapons be useless against certain enemy types since forever? I mean, if you use a rapier and you come up against a skeleton in DnD, that's bad news bears for you, since you literally can't do any damage.
Complaint Number 2 - Through NO fault of your own, your character is fucked. Go home and cry to mummy!
DND games are party based, so if a character can’t damage a certain kind of enemy, there’s other characters that can shoulder the load.
In a single character RPG, however, having certain types of characters that can’t do any damage to certain types of opponents is just stupid. It’s realistic, but just stupid. Say, for example, you were playing a game similar to Morrowind and you wanted to play an axe-wielding barbarian. Uh-oh, now you’re totally fucked whenever you meet somebody in plate armour. Using axes may have been viable in Dark Souls, but with a plausible rulesets added 'realism', you've just fucked yourself. Happy days!
Similarly, if you’re playing as an archer, you’d either have to invest a hell of a lot of attributes in strength and use a longbow, or you need to use a crossbow. Normal bows are completely useless against plate and mail. But hold on, plenty of historians argue that longbows and crossbows could only
rarely penetrate plate armour (or maybe it depends on a variety of different factors, like how the plate was made and its overall thickness and the type of crossbow.) So once again, play as an archer and you could very well be fucking yourself over.
This is obviously not acceptable. You can’t have a single player RPG which punishes you so severly because of who you want to play as. Realistic, yes. Entertaining, no.
Lastly, why are historically accurate swordfighting techniques unfun to play exactly? I would be stoked to play an RPG that implemented a European martial arts system.
Complaint number 3 - I want to use my sword!
If I want to play as a swordsman, it’s not because I want to spend half the game ‘grappling’. I know grappling was a large part of swordsmanship in the middle ages, but still, I want to use my sword! That’s why I played as a swordsman! Throwing them and 'sticking a dagger through their visor' is incredibly unsatisfying.
I have other complaints but these are the major ones.