Suggested by iKnowledge Bossk has superhuman abilities so that does mean that you really can’t count him out here. That being said, it’s still a little hard to picture him going up against Leona. She has the Orochi powers within her which allow her attacks to take on even more powerful energy properties. Bossk would really be at his wit’s end trying to counter her blows and don’t believe that he will succeed. Leona wins.
Without her Orochi Powers, I see Leona putting up a good fight, but possibly not winning against Bossk. She could end up looking scarred and savaged as a result of the above.
Bossk is a pretty impressive fighter. Leona is definitely helped a lot by her Orochi abilities, otherwise she would be more of a standard fighter so it probably would be hard for her to do a whole lot against him. She can’t afford to let her guard down for a minute