In a tank v. tank engagement, yes that’s true - assuming you fight to the death, you have a 33% chance of surviving, as does the other side.
The less confusing way to look at it is this:
Possible outcomes:
33%: Attacker lives, defender dies
33%: Attacker dies, defender lives
33%: Both attacker and defender die.
Your conclusion is confusing the way you wrote it - it sounds like the results are lopsided. Rather, both sides have 2/3 chance of getting killed, and a 2/3 chance of killing the other unit, and a 1/3 chance of surviving.
In effect, the results are a wash. However, this is more likely:
Attacker: 2 Inf, 1 Art, 1 Arm. v. Defender: 1 Arm.
Average battle duration: 1.2 rounds of combat
avg. # units left IPC value Punch
Attacker: 3.4 0.6 13.1 1.9 7.3 0.7
Defender: 1 5 3
Surviving Attackers
Surviving Defenders #Casualties
Overall %*: A. survives: 99.9% D. survives: 0.1% No one survives: 0.1%
In this attack, Russia comes out solidly ahead in retaking Archangel, losing 1.9 IPCs to Germany’s 5. Although I would probably have the UK kill that tank with a battleship anyway.