"What exactly is your power level?" Walker had realized that William was strong, but he still had no clear idea of just how powerful William was.
Certainly more than a Demi-God level!
"I really don't have a power level," William said. "All I can say is, I don't really like to fight,it's boring."
Walker, having finally asked, of course couldn't just let it go at that. He needed a reference point, so he hesitated before asking further, "Then, are you more powerful than Amy's masters?"
Without hesitation, William replied, "If we're talking about combat power, I'm a bit stronger."
...
Alright then!
Walker now had a rough idea of William's power level.
Isn't the whole point of classifying Soulmancers by power level to distinguish the strong from the weak?
Amy's masters were famously powerful. If William was even slightly stronger than Zeus and Poseidon, that would place him beyond the power level of high-ranking god-kings.