@Nutz, I disagree with him becoming strong. He was weak compared to all the powerful demons around him and so he thought he was a weak demon.
When he was forced out, he understood his misunderstanding, he was not a weak demon, but rather, a strong, if not gifted, human.
Demons excel in magic, but don’t appear to be particularly any stronger than humans in terms of physical strength. Humans, can excel in one (usually) of four techniques/weapon skills that demons seem unable to. He never checked for those techniques because he though he was a demon, so he never knew where his (fighting) strength really was.
That said, I do agree with you in his other abilities, to interact and cooperate with everyone else.
On a separate note...
This chapter shows what’s usually typical of demons in various stories. They rely on individual strength, blind to pretty much everything else. That Heavenly King can become just as powerful as his father, but his father still needed someone to “work the background,” which again, the HK is not realizing.