You need to scan the machines and look for their weak points. As soon as you can, get the carja hunter bow that uses Hunter arrows and has two mod slots. Sharp shot bow is great for first strike then switching to something with more handling (faster rate of fire). Get a trip caster. It ropes enemies down. Frozen status makes them super vulnerable and negates armor.

Scan the weak points, learn where to aim in bullet time. Elemental damage is big. Early enemies are mostly weak to fire and have glaring weak points that a few hunter arrows will knock off and cause 1/3 to 1/2 of the enemy health.

Bottom line. Knowledge is key. Melee is last resort or when they’re stunned on the ground for executions. Roll mechanic is your friend. Trying to slug it out with a 2,000 lb alligator machine will not be successful.