Recently I've been lurking about the internet and reading, once again, about how the mundane classes don't stack up against the mystic ones as DnD approaches level 20. Usually when I start thinking about this I try to think of ways to change the game to bring casters in line with the mundane classes. I like low powered gritty fantasy usually so thats the way I tend to skew things.
But yesterday I started thinking about how high level play has historically been portayed in DnD. Its got plane hopping, consorting with gods, demons and all kinds of outsiders, massive monsters and game changing magic. Given this back drop casters that are able to manipulate time, summon angles, and create mansions out of thin air seem pretty reasonable. Its the guy who can still only move up and attack that seems out of place.
So why is it that even at level 20 fighters and their ilk don't get to do awesome stuff? Why can't "mundane" classes do epic things?
Designing 'mundane' classes is always extraordinarily hard compared to designing classes that can do anything mechanically you are willing to justify. Mundane classes are forced to adhere harder to casual versimilitude and casual realism than a class which gets to opt out of realism by default. Also when you create a mundane class, you are under some pressure to create a class that also works in a setting without magic. If someone wants to run a D&D game in the real world antiquity (and no magic), then you don't want to force them to use a class where magic is implied. And its inherently hard to balance mundane with magical without making the mundane feel like just a variant spellcasting class - especially at higher levels.
First, I think it needs to be realized by designers that above about 6th level, you are no longer talking mundane. Above 6th level, you've at least moved into the realm of 'action movie hero' where falls which would kill or cripple a mundane person cause minimal injury, and traumatic wounds are recieved without anything but momentary discomfort. You've entered the realm of Rambo and John McClane (from Diehard). Therefore, if games are set in antiquity without magic AND the DM is also allowing for high level play, then you are also entering into the power level of Samson, Heracles, Achilles and the like regardless of whether magic is available. A 20th level fighter is not equivalent to a mundane hero or champion.
Second, recall that in 1e, the official title of an 8th level fighter was Superhero. I think that there is a lot too that. I think the answer for what a high level 'mundane' character looks like is a Superhero 'Brick' type character. That is, high level mundane characters need to possess superhuman speed, durability, strength, skill, combat ability, and the like. For the most part D&D gets the durability right (especially in 1e) and does ok on the 'combat ability', but it tends to miss out on the rest. Further more, especially since 1e, there has been less recognition that for there to be balance, the mundane class must exceed the magical class in its own areas by as much as the magical class exceeds the mundane class in its areas.
In general, in all editions of D&D one of the problems has been that spells are not balanced with mundane skills because the spells typically do not reference the skill system. The classic example is 'Invisibility', which at just 2nd level, grants you near absolute advantage in stealth compared to the editions equivalent skill system - say 'Hide in Shadows' of 1e or 'Hide' or 'Stealth' in later systems. So one of the things you have to do is begin to pull back the power levels of spells that tread too much into areas that should be seen as the province of the mundane. A thief or rogue can't be extraordinary, if the spellcaster can greatly overshadow their competence with the application of a few simple spells - fly for climb, invisibility for hide, knock for open locks, etc. At least some of these spells need to be placed on a more level plane with ordinary skill use. Secondly, it must be assumed that high level application of skills allows for extraordinary capability will before the high epic levels. By the time you have 18 ranks in a skill, you should be doing superhuman feats. Yet all too often we see merely ordinary things - like standing up from prone without requiring an action - being limited only to mundane characters of God-like level (without spending yet other of their few and limited resources).
This means things like the DC of walking on water using the balance skill is probably closer to 35 or 40 than it is to 90 or 100.
Another problem is that D&D in general has only treated skills as the application of ordinary ability. If you look at NWP's or Skills (in any edition), there is the assumption that skills are of minor utility. Nothing says this more clearly to me than 3e's decision to price magic items that enhance skill checks as very minor items (never mind that this occasionally causes imbalance even in 3e). A few skills were introduced as class abilities that actually have great utility, but for the most part you can only get utility out of skills by using alternate rules and even then spending your limited resources (on feats or 'skill tricks').
What is actually needed in my opinion is to increase access to skills in the mundane classes (across the board) while providing for them skills that actually matter and are desirable. For example, a 'Run' skill that increases your base movement rate, so that at higher levels your 'mundane' character can move faster than a speeding war horse. Or, for example, a 'Leadership' skill that allows your 'mundane' character to counter the effects of certain magical debuffs (fear, most obviously) and otherwise bolster those around them. Or, a 'Tactics' skill that allows various buffs for yourself or your allies. That is not to say that these skills need necessarily compete directly with spells in power, but they should be able to compete with a combination of some power and greater availability. If you have the skill, you can use it all the time. Maybe 20 ranks in 'Stealth' or 'Hide' isn't quite as nice as being 'Invisible', but it ought to be approaching that level. Maybe 20 ranks in Jump isn't the same as flying, but you still ought to be able to leap (small?) buildings in a single bound. And so forth.
Once you accept the notion of high level mundane equals 'superheroic brick' - including Captain America, Hulk and not merely explicitly (but not really) mundane Batman - then I think you've begun to unfold how you make work regardless of edition.
