Rank Conferment
It was evident that not all the Demon Rulers were on friendly terms with each other. They had their factions, but they were usually wise enough to prioritize Gozon over their internal disputes 90% of the time.
Now, however, was one of the remaining 10%—a moment when personal grudges took precedence, as the issue at hand wasn't significant enough to threaten the stability of their Interstellar Empire. As McEnda II noted, many who opposed Alvey did so simply because of his association with him.
He was the one they didn't like, but they couldn't take out their grudges on him since he was the strongest Gozonian in the Universe after his parents, so they resorted to petty methods like this.
There were two 'Supreme' Demon Kings because Jamie was around, but if Jamie wasn't, then McEnda II would hold that title alone. Even Malorum who was the Main Entity of the universe governing the Aspect of Destruction would be hard-pressed to win in a fight against him.