More armor (or more stamina in the same armor)
I'm operating on a couple of assumptions here. 1. The assumption that the phrase "the ability to reduce the pull of gravity" is meant, literally, as the only form this ability takes, ruling out changes to direction of gravity or increasing it, etc. 2. I also assume that "Fantasy setting" is meant to indicate medieval-ish tech levels, swords, spears, armor, sheilds, etc., and the 'warriors' are knights, foot-soldiers, barbarian(trope), and the like.
Leaps in combat are overrated (in my opinion). They are cinematic but, outside of very specific and rare circumstances, leaving your foundation (feet on the ground) for striking and defending is not generally a good idea in a melee martial art, with or without a weapon. You lose the ability to change your own direction and become a more visible and more predictable target, etc. So while a select few might specialize in this type of thing, I don't see this as being the most common warrior type among those with this magic ability.
In medieval battlefield combat, the guys in the heaviest, highest quality, fullest coverage, armor were the tanks of the battle. Not as slow as many people think, much harder to kill than many people think, but their downside is they run out of gas faster than standard grunt soldier, due to carrying around more steel. They make short work of anyone with significantly less armor that does't outrun them, our overwhelm them with numbers. They take heavy hits from most standard weapons (spears, and occasionally swords), and shrug them off and keep right on fighting. They make good use of those same standard weapons against those less armored opponents, and have some of their own special weapons (mace/warhammer) to deal with others like themselves in heavier armor. This is the type of warrior that I see being the main adaptation by those with your magic ability.
But in your scenario, I see 2 variations of upgrades to these "standard" knights:
The stamina knight - the downside to the amazing defenses of amazing armor is mostly in how fast the wearer gets tired (overheating is a close second and, in some cases might be considered as part of the tiring process). But with this ability, the weight of the armor is offset, at least to a large degree (exactly how much isn't clear based on the wording of the question), by the magical ability. So the wearer can continue fighting much longer than the standard knight could, with the same armor and weapons. They could also be carried for longer times or larger distances by a horse, because the horse would feel less of their weight as well. These knights would be the skirmishers of their battle group. They would endlessly harass any enemy that didn't put them at risk of being overwhelmed by numbers. For less armored enemy units, they would pick and choose targets that they could move in, take a good shot, and move away, pick a new target and repeat. For enemy standard-knights, they could harass with attacks and withdrawals until the enemy tires and eventually collapses from exhaustion, and then move in for the kill.
The "standard-knight"-buster knight - These warriors would be in heavier than normal armor. This would reduce their stamina back down to at or near the level of a more standard knight, but would offer incredible protection by medieval standards. They could confidently walk up to an enemy that is wielding a weapon specifically designed to penetrate normal knight armor (mace, warhammer, some polearms with hammer or spike elements, etc), take a hit from those weapons, their improved armor would shrug off the hit, so they can close in and end the fight. This would work, even against an enemy knight, as they wouldn't be any better equipped to penetrate the thicker armor than their less armored allies, and would be plenty vulnerable to mace/warhammer/etc strikes.
As far as weaponry, I don't see a whole lot of variation here, except that they would be able to wield heavier than normal armor busting weapons.
As far as actual fighting techniques, I don't see much variation here either, except that, especially when wielding those heavier than normal armor buster weapons, they would favor upward strikes. This is because even if the weapon 'feels' lighter, it still has the same mass, and so changes in the weapon's directions relative to horizontal travel will still be just as difficult for the wielder as if they had no magic ability. So sideways strikes with a heavier weapon would be slow and awkward, hard to start, hard to stop, hard to change direction, etc. Downward strikes wouldn't benefit from the lightened gravity, but upward strikes would. I imagine a lot of over-sized war hammers, swung like golf clubs, smashing through shields, and denting the armors beyond the busted shields, all in a single swing, due to sheer momentum so easily generated in the lightened gravity.