Ye Chenfeng did not use the Sky-Breaking Divine Beast or Thunder Kill.
The Sky-Breaking Divine Beast combines the Fire Sword Intent with the Phoenix and Qilin Profound Meanings. These two Profound Meanings are a bit inferior to the Ice Dragon Profound Meaning, but when combined, they are stronger, giving the Sky-Breaking Divine Beast more power than the Dragon Soars Nine Heavens.
As for Thunder Kill, it draws on the power of the Nine Heavens Mysterious Thunder from the Sea of Consciousness. The more it's drawn, the less power remains. Ye Chenfeng didn't want to waste Thunder Kill here.
