and, a few days later, JPMorgan emerging as one of the most active buyers
I'm sick of this claim. It was one of JPMorgan's
clients. There's no evidence that it was JPMorgan themselves buying BTC. The bank doesn't have to agree with everything that their clients do.
It's more likely that Dimon was just annoyed about hearing about BTC so often, so he tried to get people to stop mentioning it to him. Unfortunately, he did so by irresponsibly lying about BTC being a "fraud".
He did manage to bring down the price for about over 20% so was it worth it the reputation?
If it was manipulation (which it most likely wasn't) it was worth it. It's not like he had much of a reputation to start with.
Will anyone beleve him again?
After he
did this, no intelligent person believed him anyway. Idiots might well continue to trust him.