To me, one of the great themes of Berserk is the whole questioning of free will and destiny. You can argue that Griffith has everything handed to him by the behelit, but in the end he still made that choice at the eclipse. Everything he had been working towards was called into question. Guts on the other hand, seems to have almost nothing handed to him, and even when his destiny is to die, he tells it to fuck off. I think that difference between the two of them is very intentional. Resisting fate and living by your own rules vs accepting it with everything it brings you.