When Amon's old tamed beast, the Great Sun Hawk, died by self-explosion using its life force, the resulting blast nearly killed a much stronger spirit beast. What Altered Yuka did now was the same, except it was not a simple explosion by detonating its life force. Altered Yuka was in the middle of using its light-and-darkness explosion, a move that was extremely destructive on its own. Detonating its life force amplified this already powerful move even further.
Hence, the resulting explosion was one even Amon didn't anticipate. He was within the blast range. He didn't have time to flee the blast zone due to Wu Di and Zin Gang's interference.
In the past, he survived Yuka's light-and-darkness explosion by using the defensive art of his lightning flying knives. Those knives were gone now. He was stronger than then, but so was Altered Yuka. Furthermore, the explosion was augmented by sacrificing Altered Yuka's life force. The destructive power couldn't be compared to before.
