Even then Zodd did better : first he didn’t go all out at all. Secondly he put Guts on his last leg just to have an injury. Guys had no possibilities to take down Zodd
Zodd himself actually portrays it as if he was genuinely damaged
I watched the 90s anime, it's said nowhere that zodd held back
Guts was not able to damage boscohn until zodd saved him
In other words. Guts on his own did more versus zodd then boscohn