there was already enough force to defeat 3 Yonko present in Wano, and he was willing to fight them
1: Luffy+Jinbei
2: Law+Kid+Sanji
3: Yamato+Zoro+Killer+Scabbards
and he runs away from Momonosuke ?
or even if it was Shanks, he should still fight him... Shanks is nothing when compared to 3 Yonko