"solving" Dota is a huge huge HUGE overstatement of the kind you are pointing out.
The players it played against had never played against something that behaved so weirdly. It had lightning reflexes and it clearly wasn't human. It was playing a toy game mode requiring about 5% of skills needed for a full match. I'm other words, they engineered it to look good at they toy task, and it did. But they didn't give the pros any time at all to learn their opponent -- after all they might have figured out how to play against it!
Not arguing that they solved DOTA, but "The players it played against had never played against something that behaved so weirdly." seems like a feature, not a bug. We want AI to find unexpected new ways of accomplishing tasks.