The context of the term "hyper lethal vector" is literally unknown. It's obviously a group of words that sound awesome, but does it really mean anything? Is it an actual classification? Or is it just a term Halsey decided to use? My take on the whole matter is that it's a fluff term used for Reach's marketing to hype people up as playing as a super skilled assassin soldier. In fact, looking at the existing lore, it doesn't really make sense that Chief would be classified as a "hyper lethal vector" because while he is ridiculously skilled, he never really excelled in anything (more than any other Spartan) other than leadership. And even then, Kurt was determined to have been a better leader than John.