Aarn is certainly a high-magic setting, I will not deny that. However, a major goal I've had since the beginning is for a character without magic to survive and remain competent. Magic, while powerful, is largely in the setting for flavor and for convenience. It is a utility, as much as a utility as rope is to a dungeon-delver.
Magic can enhance characters' abilities, and can help characters deal more damage and absorb more damage. Magic can do many things. However, it is not as important as a character's skill. No shiny magical armor or flaming sword will make a farm-boy become an epic hero overnight. He'll get creamed no matter how powerful his equipment if he rushes into danger carelessly.
When it comes to a character trying to avoid magic, their physical abilities quickly climb into the superhuman level of ability. Many things in the setting strive to be realistic, but I suppose a man must be allowed his guilty pleasures; imagine a completely non-magical adventurer who can leap 20 feet in the air, effortlessly fell a tree in one swing with their sword, plow through a battlefield like a runaway train, tossing his or her enemies aside as if they were tissue paper.
It is not the job of magic to further enhance the abilities of this dreadnought warrior. It is the job of magic to allow jacks of all trades to compete on the same level.
As an example, spells that increase someone's strength do not add a modifier onto the ability score. It simply doesn't stack. Instead, the spell will change the ability score to a set amount. A character with a strength of 3 and a character with a strength of 1 will be given the same maximum strength, 4, if they have a spell cast on them that will raise strength to 4. Further, characters with a strength of 4 or higher won't be affected by the spell at all, even though it is still technically affecting them.
Magic, because it doesn't stack with natural abilities and only supplants them, can be seen as an unnecessary distraction to more serious warriors. Having a handful of magical items, such as a suit of armor that allows them to have a wider range of motion, or a sword that deals more damage with every swing will certainly help them. But not having these items will not handicap them either, and they have natural skills they can learn that produce much of the same effect.
Further, all characters will have a magical resistance skill. This skill represents how toughened and resilient their magical aura is. How much punishment the aura is used to taking. The higher this skill, the easier it is to not only resist magical effects and magical damage, but also elude magic that can detect life, detect thoughts, etcetera. For all its bells and whistles, and its "ooh" and "ahh" effects, magic is capricious and can be nullified somewhat effectively if one is properly prepared.
And that's ignoring the aforementioned wizards whose specialty is nullifying and countering others' magic, including their magic items.
I'm also contemplating adding another skill which represents a character's ability to use magical items. The higher the skill, the more items they can use at once, and the more powerful those items can be. It would essentially act as an item-wealth level-limit, as seen in many, many other rule settings. I may or may not include this option depending on how much it is needed once I reach the play testing phase.