There still seems to a big difference between Guts and Serpico. Serpico stated, in their scuffle at the Tower arc, that he has a feeling he won't be able to beat Guts in a straight fight, and that was before he admitted how he didn't think Guts was in so much of a super human level. Not to mention Guts' armor not even giving signals of taking him over, implying Serpy wasn't that much of a threat. Still, serpy should win this without much problems considering 18 years old Guts was already Griffth's equal, maybe even stronger, and we have a clear chain of Guts [vs serpico] >>> Guts [19 years old] >> Guts [18 years old/vs faggith].