Malevolent Weak Minds Theory
During first season, the king was able to exert a sort of passive influence over the people around John and Arthur to make them go crazy and attack them in a rage.
This seems to stop in the later seasons, with Arthur saying he thinks the King gave up and isn't after them anymore. No one else flies into a manic rage in Arthur's presence.
However, there is a different emotion that characters seem to feel very strongly out of nowhere.
Oscar, whose only previous experience with Arthur was being threatened by him, trusts Arthur enough to tell him about his traumatic backstory and is literally calling Arthur "his purpose" within two days of meeting the guy.
Noel immediately trusts Arthur despite hearing him mere minutes ago admit to "at least" seven murders.
The Butcher literally says he falls in love with his victims and switches to Arthur's side after Arthur got him jailed and prodded at his Daddy issues.
I think the people around Arthur are still being influenced... but not by the King in Yellow; They're being influenced by John.
John's emotions for Arthur are literally spilling out and effecting those around him to trust him and seek guidance and tell him what a great guy he is, that he's special and amazing. It explains why so many different people and entities get immediately obsessed with Arthur after just one meeting. It's because John is obsessed with Arthur.
And you call it madness... ah, but I call it love.
