I think the point is more that the model they've built can clearly learn a hero and play it better in almost all cases than a human

I don't agree, at least not based on what's been shown publicly. OpenAI can play a hero excellently in all cases where the only heroes in the game are the 17 that have been chosen and trained against. For another way to phrase the argument: with 17 heroes, there are 6188 possible lineups. Just over the course of this weekend, they'll have played about that many games. But when adding the 18th hero, that number doesn't go up linearly- it goes up by about 40%. What happens when you double it, say to 34 heroes? Suddenly there are 278,256 possible lineups: 45 times more than what the AI has trained with for this event.

With the full hero roster, there are 167,549,733 possible 5 hero lineups. So for this weekend, OpenAI is showcasing its mastery of 0.0037% of all possible Dota2 lineups. It's absolutely an accomplishment- but it's not Dota2, not by a long shot. Each of these lineups has nuances, similarities, and differences to others that human players have to determine and evaluate on the fly (often having never played a given 5 hero combination together). The AI doesn't- it's played plenty games with each of these lineups and against each lineup it faces.

Another problem is that some of the ways we've seen the AI gain an advantage is through things that aren't at all related to intelligence, tactics, or strategy. Calculating the maximum damage of three spells and an autoattack to an exact value against a given magic resistance and armor isn't "outplaying" a human, it's just out-mathing it. Reaction times were another issue- I know they've tweaked it multiple times to be more accurate, but human reaction times have a variance that players need to account for. You can't just automatically rely on hitting a perfect BKB against a Lion blink->stun because Lion's cast point is 0.3 and your peak reaction time is less than that... that's not realistic at all.

If they've simply chosen to adjust their priorities based on what they've accomplished in Dota2 already, that's understandable. But phrasing that as if Dota2 has somehow been conquered when literally 100 heroes have been ignored (including all of the most complex ones) just seems ridiculous to me- certainly more marketing than science. I'd love to see an article on why they feel that the gap between 17 heroes and 117 heroes is so easily bridged just by throwing hardware at the problem, and what kind of specific training they have to do for each new hero that's introduced.