Go to Ministry . Get Frostdraw to 20. Farm the golems. You finally unlock Lumbering Slam . You can now kill a golem in 3 hits. Farm the Adret tribe for Meditation to swap mantras easily.
But claiming a heavy weapon is "the best" is nuanced. The "best" build depends on your goal: wiping a Chime of Conflict leaderboard, tanking a Diluvian Mechanism wave, or surviving a Voidwalker gank. best heavy weapon build deepwoken
Use Crystal Road liberally. The crystals block projectiles. Walk forward slowly. Do not run. Force them into a corner. One Curved Blade M1 catches their dodge, and the combo is over. Go to Ministry
Curved Blade of Winds (Halberd). It has extended range, a horizontal swing, and deals Slash damage, which few armors resist. You finally unlock Lumbering Slam
Gale (+Weapon speed). You need swing speed more than damage. Never use "Heavy" enchantment; it makes you unusably slow. Mantra Loadout (The "Ice Giant") Frostdraw + Heavy Weapon creates a "turret" playstyle. You freeze them, then you crush them.