With over 10 000 hours of Dota [1] under my belt I am fairly certain that even with perfect mechanical skills [2] a strong human player will still beat the A.I.
Even at the very top pro level, matches are constantly being won & lost purely based on the initial hero drafting phase. Calculating the optimal draft is way more difficult than Go. It's probably not an exaggeration to say that the search space scale difference from dota draft to Go is about the same as from Go to tic-tac-toe. Because it's not only about the 100+ different heroes grouped into combinations, but also every possible game that can happen then with those combinations.
Then once the game starts, the A.I. may be able to respond to actions extremely quickly, with perfect precision. But what should the responses be? This is not a simple thing to answer and humans keep taking completely different approaches as our understanding of the game keeps evolving.
Also, the very best dota bots can currently only beat absolute beginners who don't understand the game at all yet. It takes a few hundred games of practice for a human to go beyond the best A.I. currently available.
--
[1] A game similar to League of Legends
[2] Directly reading from memory and then directly calling gameplay functions, basically a perfect hack, would get you what is known as "mechanical skills". For example being able to last hit.