Perhaps? With no evidence, it strikes me as a crime that is not weighed in ROI terms; it’s people with a sick compulsion, and I have always believed that kind of thing isn’t affected by the severity of possible punishment. I’d be interested in data for sure.

With no evidence the proper assumption would be no assumption.

But evidence was presented child sexual abuse declined since 1990. The question was how to explain it.

Punishment severity doesn't much reduce child sexual abuse probably. But not because it's a sick compulsion. Punishment severity doesn't much reduce most crimes. Financial crimes included.

They mentioned chances of being caught also. Punishment likelihood is an effective deterrent generally.

Pornography could be a factor. Many studies found rape decreased in countries when pornography became more available.

You're way off but I don't feel like taking the opposite side of this argument. If you want to research this there's plenty of data and information available.