I'm not proficient in Starcraft, but if they have to make Pros play against 5 different agents for a Bo5 is it because the same agent would merely repeat the same game overall and the human player would be able to see through its strategy?

AFAIK at least for Go/Chess DeepMind wasn't handpicking agents to send against human opponents, but it was simply a trained agent who would try its own strategy and respond to the opponent, in this case isn't it like the single agent only ever plays a single type of meta strat? If so, I think this is a bit less impressive than what I had predicted.