I honestly have to reread the fight, but yeah it was said Kuroro wasn't trying his best. Zeno wasn't, either. Going by a gut feeling, Zeno wins... Kuroro was pretty surprised overall with Zeno's fight prowess, constantly saying "what an awesome old man..." iirc. Zeno and Silva probably went at him together due to them being overly cautious and making it sure they'd win the fight. But yeah, I think Zeno alone would defeat Kuroro high diff.