Nuke Em all! More! More! More!

Focus on atk speed, atk dmg, crit chance and aoe for higher dps. The higher these stats are the faster you'll melt a boss.

My setup is always 2 same hand weapon (default character weapon): Fission Device (+projectiles), Propulsor (projectile speed) or Mutator, Cooler (atk spd), Power Booster (atk dmg)

2 Gravity Cannon: Fission Device (+projectiles), Amplifier (bigger aoe) or Expander (duration), Cooler (atk spd), Life Recycler (heals for a portion)

2 Sattelite Cannon: Fission Device (+projectiles), Expander, Cooler (atk spd), Power Booster (atk dmg)

You can use other weapon such as Booby Trap. I tried other weapon but i find AoE weapons viable since it can hit more enemies.

Lv3 Damage Immunity
Lv3 Emergency Shield
Lv5 Survival Boost
Lv5 Combat Boost
Lv5 Agility Boost
Lv3 Defensive Measures
Lv5 Exp Boost: fast level up for upgrades
Lv5 Potential Cost Reduction
Lv1 First Aid: just in case you accidentally die
Lv5 Starting Funds: you will have +150 crystal at the start that allows you to unlock all enhance slots for left weapon.
Lv4 Weapon Boost: gives you a maxed out right weapon

Not much in here! Just max out the +weapon atk dmg, crit multiplier and crit chance.

Prioritize the following enhancement as soon as it shows up:

Aggressive Neurotoxin: Crit Mutiplier and Crit Chance
Active Neurotoxin: Crit Mutiplier and Crit Chance
Supercomputer System: XP multiplier and Luck
Technique System: XP multiplier and Luck
Power System: Movespeed and Dodge

Prioritize the following relics and the rest is up to you.

Holographic Defense: invincibility duration after taking dmg
Heavy Exoskeleton: boost atk of main hand weapon
Link Core: buff when you have 2x same weapon
Health Type A: Atk power for weapons
Energizer Type A: Atk Spd
Counterweight Stabilizer: Crit Chance
Longshot Ring: Extra damage to enemies outside the ring

This is just a guide and there might be some mistakes but I hope this will help you. You can do some trial error and see what works for your play style.