Authority was the only word that Roy could think of currently.
After becoming a demon lord, Roy found that although the difference between demon lords and high-rank demons was only one hierarchy, the feeling they gave him was that they were two completely different beings. Advancing from high-rank demon to demon lord was a qualitative change, so the same logic could apply. The gap between demon lords and demon kings should also be ridiculously large.
Demon lords were called demigods, but demon kings were true gods. As existences like gods, demon kings definitely had some extremely powerful and irresistible power. Roy suspected that this might be the so-called authority.
If his guess was right, and the so-called 'Gluttony' ability was Beelzebub's authority, then he indeed could not easily obtain the power of such authority from the shell.