Part of this was thanks to the presence of Tina in that little team. Even if the two tried to deny it, they got some sort of spark going on between each other. And in the end Ibra always pushed himself over the limit, even when he was training with William whenever Tina was present watching the show.
William didn't have any intention to watch them, but he already released his two weapons and let them fight with them. Yet at some occasions, he lost focus and couldn't track what was going on, just like the time when they got totally surrounded.
He was busy making these formations and arrays. But once he got done, he turned around and made sure his two deadly monstrous weapons would kill lots of these Wrathers for an entire hour.
During the last fight, he entrusted recharging his two weapons using elixirs to Ibra and Berry. The two learnt how to do it, and that saved William lots of trouble.