When Cleric sees Wutteat in the Coffers he outright says "This is where I am meant to die." or something along those lines. Cleric was done.
I think Akka is definitely among the absolute top of human sorcerers. I suspect that surviving Quya, Dunyain (or half-Dunyain), and the Twins probably outclass him. Of course "power levels" is kind of bullshit anyway. Just because someone might beat Akka in a fight 9 times out of 10 doesn't mean that the die won't occasionally come up a 1. And there's things to think about beyond raw power. Before he became Shauriatas, Shaeonanra wasn't known for the power of his sorcery, but for the unconventional subtlety of it. In a shoving match, others were stronger. But he came up with weird loopholes and tricks that made him the most formidable man in his School. This kind of thing is hard to quantify.