IIRC, amongst banned heroes were key splitpush heroes such as Nature's Prophet, Tinker and Phantom Lancer, which are a known counter to the early-game advantage

IIRC, amongst banned heroes were key splitpush heroes such as Nature's Prophet, Tinker and Phantom Lancer, which are a known counter to the early-game advantage, mid-game push strategy that the OpenAI 5 executed. Early-game laning and mid-game teamfight combination are micro-intensive, and consequently the biggest advantage the OpenAI 5 had over OG. Against the simple AI that comes built-in to Dota 2, you can be behind by a ton and exploit splitpushing against the AI, because doing any structural damage against buildings will force the AI (who are gathered up for a push) back, and you will still win if you drag the game sufficiently into the lategame. Deciding whether or not to continue to push and which heroes to send back to defend is one of the hardest strategic decisions to make in the game, even for humans. The finals of one of the TIs, NaVi vs. Alliance, was lost on getting such a decision wrong. Eliminating some key splitpush heroes minimized the probability that OpenAI 5 would have been forced into having to make such a decision. It would not surprise me if the OpenAI 5 would have lost against OG had the entire heropool been available, had the series been long enough or had the prizepool been big enough for OG to take the game seriously enough to warrant picking a splitpushing strategy (which is considered cowardly in some circles).