>>527680358
>>527680647
>>527680878
Now here's some math using datamined numbers to make it definitive the arc dog is just an arc thrower zap with less durable damage
The arc does 250 normal damage and 45 durable damage. The liberator does 85 normal damage and 25 durable damage at 2 penetration. A brood commanders head has 200 HP, 60% durability and 2 armour

The arc does 127 damage to the brood commanders head
(250*(1-0.6))+(45*0.6) =
100+27 =
127 final damage
A single zap puts the brood commander head at 73 HP remaining

The liberator does 26 damage a shot to the brood commanders head
((80*(1-0.6))+(15*0.6))*0.65 =
(32+9)*0.65 =
41*0.65 =
26 final damage
At 73 HP remaining the brood commanders head needs 3 follow up shoots from a liberator to pop

If the arc dog did 100 durable damage, the same as the arc thrower, the brood commanders head would be at 40 HP remaining after the one zap and the second liberator shot would have popped it, not the third. Here's a webm of a brood commander taking a single zap from the arc dog and then having its head popped on the third liberator shot, exactly lining up with the math from the datamined numbers