I think the GP means that the AlphaStar team stopped working on the project because they felt it was reaching a dead end and unlikely to produce further results, or at least other ventures might have been more promising.

I think that's most likely the case too, otherwise why would they give up?

I guess I feel that there is a big discontinuous jump between "not clearly better than humans" and "clearly better than humans," where the latter is much, much more significant than the former. It seems like going on a hike and stopping before the summit.