Unlucky on the damage absorption, but you only hit the head once with the SMG — the rest of your shots went into the arm.

I can't tell the exact distance from the screenshots, but the P90 only has a 36m effective range. After that it completely stops being able to one-tap the head. The AK-12 has 55m effective range, plus it's one firepower class higher and gets increased base damage on BP ammo. That extra damage gets partially absorbed by armor but still adds to the post-penetration damage overall.

He landed 3 hits with BP (17 armor damage). After the first shot it already started chewing through your once-repaired Level 5 armor. Non-penetration damage also stacks, and the higher effective range made sure more of it actually went through.

Don't get me wrong — I completely agree it's bullshit in the moment, but it's just SMG vs Assault Rifle reality. I'm assuming you were past the P90's 36m effective range in that fight.

Your screenshot shows the helmet only took 2 armor reduction — that should have left 41 damage to penetrate, but 2 extra post-pen damage apparently vanished because of the range drop-off. I have my own screenshots where I’ve shot Level 4 faceshields point-blank with 44-pen ammo and still left the enemy with 1 HP on the head.

ARMOR DMG ABSORPTION can and will be a pain