Sure a KING KONG BAZOOKA could have blocked Hakai, but at what cost? they didn't know about the magic drug, and they knew they needed to fight the yonko.
Luffy couldn't risk getting injured like that as he is much more important to the alliance than Zoro, as Yamato in this very chapter illustrates to Momo, that LUFFY is fighting the king and putting WANO ON HIS BACK.