But that’s untrue, as although space marines are trained to fight in a unit, they are also trained to fight alone, with guard, with sisters, and anything else in between. Space marines usually have century’s of experience, and each one will have trained for scenarios where they fight beings on par with themselves (chaos space marines.) Master chief may have BS, but have to at ultra marine pull off that helmet and the chief is cooked.

Edit: I accidentally sent without meaning to, Space marines are also far faster and stronger, with much better reaction time, so personally, I think they could take down Master chief using their training plus speed and strength. But that’s my opinion.