Heathcliff is a pretty powerful fighter since his defensive abilities are very overpowered and practically aren’t fair within the Sword Art Online framework. That being said, Kirito has been shown to be skilled enough to get past this barrier. His sheer speed and strength are simply that far ahead of the pack and Heathcliff can’t hope to block fast enough. Attacks will always get through a defense eventually and this is no exception. Kirito wins.