Stalkers have 14.4 DPS (vs Armored units) while Immortals have 48.1 DPS (vs Armored units). Both Immortals and Stalkers are armored.
Immortals provide more than double DPS, with 200+100 HP / Shields. While Stalkers have only 80+80 HP / shields. Stalkers cost roughly 1/2 of an Immortal, but any "even match" would have roughly 2x Stalkers for every Immortal.
Immortals do roughly 3.5x more damage while having 2x the HP (Immortals have a bonus ability to gain +100 Shields as well). Even if outnumbered 2-to-1, Immortals shouldn't lose the fight.
The problem is that AlphaStar can watch all of its Stalkers's HP simultaneously, and blink them away from danger instantly. AlphaStar is playing a game that is fundamentally different than what Humans play. In AlphaStar's version of Starcraft, Stalkers win vs Immortals. All you gotta do is Blink away low-HP Stalkers to the back line, and then have the Stalkers regenerate their shields before bringing them back into battle.
Its inhuman. Maybe its intelligence, but its an exceptionally poor demonstration of intelligence.
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The game that the AI played was not Starcraft, certainly not the game that humans play. Humans cannot physically click quickly enough to move stalkers in the way that AlphaStar did. The screen humans look at cannot show all of the HP of your individual units. The screen humans look at can only see some of the battlefield, not the entire battlefield.
That's the main issue with the demonstration. Sure, the APM rules were designed to prevent this situation from happening, but the demonstration proved that the APM-caps were insufficient at creating human-like playing conditions.