See "The Marginal Advantage," an essay from the famous Starcraft player Day9: http://www.teamliquid.net/forum/brood-war/64514-competitive-...
I meant to say that strategy trumps mechanics. Mechanical proficiency is necessary but not sufficient.
It's also worth noting that AlphaGo optimizes its perceived chance of winning the game, rather than its score. It "gets complacent" and mostly plays very conservatively the moment it's ahead on points, because it doesn't care about margins, only about win/loss.
Additionally, humans can use economic reasoning (player built 3 barracks to they can't be building x, y and z). This can lead to AI being excessively safe (economically inefficient).
And the last line you said is also true to make things even more difficult. :)