Reroi immediately noticed humanity's great efforts to defeat enemies and there ability to stand despite being so small and weak compared to other races in the galaxy. The Human form is a specialist in 2 handed weapons and wheeled vehicles. The same with the brute form, these forms are arguably better foes then humans could have been.They were all secretly destroyed by the Elites after one developed a connection with humans and joined them, and the Elites thought the others would soon question the Covenant.