Not true, if you read between the lines of what the grimoire cards say. Even Kabr likely didn't fight alone, at least not originally. "No one can open the Vault alone. I opened the Vault. There was no one with me but I was not alone." - VoG Grimoire card. It can be interpreted as that Kabr was not alone, originally, in the VoG, and that he probably made it a good deal in with the help of a team. However, because of how certain enemies and even the Vault itself are 'things out of time', it can be safely assumed that certain events led to him being forced to forget his team. Like the Oracles/Templar or Gorgons, means of completely erasing their victims from all existence. In other words, how could Kabr have ever remembered he had a team with him when the templar and oracles eliminated those that couldn't save themselves from 'the mark', or a gorgon's gaze wiped out whoever was unlucky enough to stumble in front of them? In short, Kabr is best known for fighting alone because nobody even [b]knows[/b] who the others were.