I really have no reason to use Older Tech. I've tossed together some numbers for a zergling, take a look:
Nintaku:
Attributes: Agility d8, Smarts d6 (A), Spirit d6, Strength d6, Vigor d8
Skills: Climbing d8, Fighting d6, Intimidation d6, Notice d8, Stealth d8
Pace: 8”; Parry: 5; Toughness: 7 (2)
Special Abilities
Armor +2: Thick hide
Burrow 4”: Zerg can almost literally “swim” through rock. Some are better at it than others.
Fleet-Footed: Roll a d10 when running instead of a d6.
Low Light Vision: Ignore penalties for Dim or Dark lighting.
Scythe-arms: Str+d6, AP 2
Size –1: About the size of a large dog. With scythe-arms.
We're assuming that Toughness 18 (12) Marine we've been discussing. So a lone zergling with a Wild Attack (used as default attack mode) would be rolling d6+2 vs Parry 5 or 6 (barely even odds), and damage would be 2d6+2 (9 damage), +1d6 if it somehow gets a raise (13 damage), both vs Toughness 16 (AP 2). Not a threat.
Five zerglings Wild Attacking would be rolling 5d6+6 to hit (Gang Up +4, read individually looking for raises), with five rolls of 2d6+2 (9 damage) and good odds of a raise (13 damage). With a maximum possible of 21, 16 being a success and 20 being a raise, that group of zerglings at least stands a chance against a single Marine. Especially an extra. No need to use lesser weaponry.
Now take a peek at my Hydralisk:
Nintaku:
Attributes: Agility d6, Smarts d6 (A), Spirit d6, Strength d12+3, Vigor d8
Pace: 6”; Parry: 5; Toughness: 14 (4)
Skills: Fighting d8, Shooting d8, Stealth d4
Special Abilities:
Armor +4: Exoskeleton
Burrow 3”
Fearless: Never suffer Fear or Intimidation effects.
Low Light Vision: Ignore penalties for Dim or Dark lighting.
Slow Regeneration: Healing roll once per day.
Scythe limbs: Str+d10, AP 2, -1 Parry
Size +4: Hydralisks stand shoulder-to-shoulder with small elephants.
Needle Spines: 2d8+1, 4AP, 24/48/96, Stun (Vigor roll or be shaken for 1d6 rounds)
Fighting D8, melee damage d12+d10+3 AP 2 (not counting Wild Attack or a raise), ranged damage 2d8+1 (not counting aiming, and I haven't given them any autofire capability yet) AP 4 and Stun. The spines average 10 damage, max 17, vs 14. They really aren't nice.
Rather than nerfing the marine armor from what it should be, I just beefed up the zerg "natural" weaponry to the ridiculous levels they're supposed to be from the narrative.