The Mgalekgolo (Covenant Hunters) weight almost five ton and can more or less take a tank round point-blank. They would plow through six Brutes as if they were humans, and their weapons would be shrugged of without much harm.
It would of course depend a lot on the setting. In narrow passages, indoors or in the forest the Hunters would win, while on more open fields the Brutes would take them down. They are faster and while nowhere near as durable or as strong, they can avoid and gun down.
IDK about that, Hunters exel in open areas, and while they arn't as fast as Brutes are, they more than make up for it in long range bombardment and firepower.
Those arm cannons have both Fuel Rod Launchers and Beam/Burst fire capability, which overshadows common brute firepower by quite a few margins.
Brutes arn't quite that tactically intelligent. Given that they outnumber the Hunters 3 to 1, the most common strategy is to surround and wittle down the opponent.
The Hunters however, can simply stand back to ack and plow through any cover the Brutes use, and smash right through them. So unless the Brutes are packing fuel rod launchers, they can't liquidate the Hunters very easily, since most Brute weapons wouldn't get through their armour.
Since the OP did not list what weapons the Brutes had, you kind of have to assume which party would win overall. Of course knowing the equipment does change the outcome, but that creates a "what if" scenario which is bad for hypothetical battles since "what if" conditions create exceptions to what "would" most likely happen. And exceptions to victory are generally bad for hypothetical battles.
Overall Hunters win because once Brutes go berserk they only do melee attacks which Hunters are basically immune to.
If Brutes get vehicles, rocket launchers, fuel rod canon's, sniper rifles, etc then the advantage goes to Brutes. But then again this is a what if scenario...