That doesn't mean he could have defeated his master in a straight up fight which is what most people consider powerful. When Malak took a cheap shot at Revan when he thought he was more powerful and skilled he even said he regretted not proving it in fair combat because it left questions. Turns out Malak wasn't stronger or more skilled.
A straight up fight has never been the Sith way. Darth Bane himself, creator of the Rule of Two, has stated several times that the tools of the Sith are cunning, betrayal, and deceit. It is the way of the Dark Side, always has been. Any Sith who believes otherwise isn't worthy of using the Dark Side. Again, this is shown by how Darth Bane handled Lord Kaan and the Brotherhood of Darkness. Also shown when Darth Bane fought against Lord Kas'im on Lehon at the Temple of the Rakata.