But did you account for the amount of torso fusion that they must and done and weapon fusion etc...
Making a simple calculation:
NPC HP = 4565
Weapon dmg = 60
Drone (Antares) dmg = 50
NPC resistance = 45
Actual weapon dmg = 15
Actual drone dmg = 5
Weapon shots: 4565 / 20 = 228,25
Best weapon dmg may be up to 80 per shot (including fusion lvl11) but weapons that deal 65+ dmg are usually using bullets or rockets and you'll run out of ammo long before you'd win the battle. That's why i took average of 60dmg per shot.
Oh, dmg per shot applies only when there's no shiled. Include the shield and you basically double the hits you will need for winning.
Since weapons use heat and NPC also deals some heat to you, i didn't include those turns needed for cooldown and/or moving into weapon's range. That also adds turns to beat a NPC.
So, in bare minimum, when facing a NPC with 4565HP, you'll need atleast 229 turns to beat it. Include the NPC shield, about 425-475 turns. Including cooldown/moving about 450-500 turns in total or so.
No matter the build you use, you can't beat that NPC i'm facing.