@Book they are not equal in strength. They're on a similar power scale, but each uses unique powers to them and depending on your compatibility you might or might not be able to deal with them. And there is one guy among yhem who is kind of like a walking nuke. This soul reaper guy uses special art that influence your mind, so if you cannot deal with it, even if you are stronger than him in sword art, he can kill you. But conversly if you counter his soul art, you can kill him easily. The heavenly deamon explained it a few chapters ago
@ISIDRO actually mc is really very close in power to her and can kill her if he really wants to. Very soon he will be stronger than her and pretty much any demon supreme in the cult.
@Book No, in terms of actual power, he could defeat the soul demon. The problem is, the soul demon basically uses illusion magic to mess with the mind, making him nearly impossible to beat, unless you can stop the illusions from affecting you.