> The way I would guess this played out was that OpenAI tried multiple variants of the game, and this version ended up being good enough to beat human players

No. We had implemented scripted courier logic for 1v1, and when switching to 5v5 the easiest starting point was to run five copies of that logic. (Dota's Turbo mode also has five invulnerable couriers.) In June, we had more important restrictions to remove — such as wards & Roshan; you personally were focused on the particular heroes we'd chosen: https://news.ycombinator.com/item?id=17392455. The couriers only become our most important restriction in August.

>strategies unfamiliar to humans.

Deathball strategy has been a thing since even before 2014...

Not with infinite regeneration. Just look how a normal Dota match plays out.

You have argued yourself into a corner. It happens.

Salves are not infinite regen and regen-heavy deathball strats with high sustain have been a thing in the past. Calling it unfamiliar makes it seem like it's a completely foreign, unexplored strategy.

That's not the point. The point is that the humans wouldn't know that regen-heavy deathball strat is optimum unless they've played that game a few times. Since multi-invincible-courier game was not available to the casters, they couldn't really prepare for it or even had any incentive to. They were paid to just play a game, not to win it, and thus they played standard Dota 2, and didn't bother theory-crafting strategies for how to optimize this weird subset of Dota.