Hey! Sorry if this isn’t your area, but I’m writing a fantasy story set in a world where people have various individual abilities (i.e. one kind of magic each). There’s a villain character with a military background who has magic, who’s fighting a character without any magic. What kind of powers could someone have that would make them really effective on a battlefield/commanding troops, but put them at no great advantage in one-to-one combat of this kind? No worries if you don’t know. Thanks!
This reminds me of a post from a couple months ago. Obviously, it’s not the same question, but might be useful reference.
Support related magic could make someone far more effective in a command position, but have little effect on personal combat.
One irony is that the D&D bard fits your question, almost perfectly. The class is a real master-of-none situation. If you want to fight people you’d be better off with a fighter, paladin, or other front light combat type. If you want to heal them, clerics and druids specialize in that. If you want a mage, there are wizards, sorcerers, and a number of other, better, magic users. What Bards do is buff party members, improving their attacks, helping them resist hostile effects, and improving their skills, while filling in on all the other roles as a backup. Being able to magically inspire your troops may sound like a pretty minor thing, but it’d be a major strategic asset. The class gets treated like a joke by the community, but in the right hands it can be very potent.
Beyond examples like the Bard, even just having an unusual attunement to sensing magic at range could be useful for tracking enemy forces that have their own battlemages.
Remember not to discount your villains who don’t fight. Someone with a military background would know how dangerous powered opponents are in their world, and would take steps to prevent being ambushed by them. Because they’re not able to leverage their abilities in one-on-one combat, they’re probably going to ensure that they’re not alone when your hero comes for them.
Without knowing what kinds of magic exist in your world, it’s a little difficult to know exactly what kind of spell list your villain may have access to. So let’s split this up a bit.
Healing magic, particularly of a sort, on the spot, healing can be incredibly potent.
Being able to augment other characters, such as boosting their attacks or defenses.
Being able “debuff” enemies, reducing the same.
Necromancy, being able to call up the souls of the dead. This one depends a bit on how necromancy works in your setting, but if it involves prolonged rituals, that won’t help in a fight, but it will let you make some friends for when a fight does come.
Wards or bindings that prevent enemies (or certain kinds of individuals) from crossing borders or leaving specific places. Which would lead to your villain being able to bind your hero to a location while they ran for help. Illusion magic could help them make their own forces appear more fearsome, or powerful, significantly impacting enemy morale, while offering limited value in direct combat.
Counter-magic is a bit of a weird one, but could significantly help your villain. It wouldn’t make them more effective in combat, but it could help to negate enemy powers. On a larger command scale, it would give them the ability to specifically negate enemy powers that would be devastating if left unchecked.
As world building goes, magic is opportunity to get creative. You decide how the metaphysics of your world work, and then create powers that fit within that. At that point, your not limited to things like lightning bolts or fireballs, and you can start creating some really unique powers, if you’re so inclined. So, there isn’t really a wrong answer here, let your imagination run wild.