Sherlock season 4: Eurus was a perfectly fine villain. So was Culverton Smith. As was Vivian Norbury.
Then Moriarty showed up out of nowhere dancing to Queen.
And you realised: Christ, none of you can live up to this ever, can you?
Because Moriarty was equally as scary and dangerous. But he was also campy and had a sense of humour.
That’s the key about Moriarty as a villain. Always was. Scariness combined with a bit of silliness.
Every villain on Sherlock after Moriarty failed because they took themselves too way seriously.