Were literary detectives only effective against crimes of violence, or would they have been successful against white collar crimes?

Absolutely, but those crimes aren’t very readable, so you don’t see it often. Murder and blackmail are much more compelling.
That said, there are examples of white collar crime being investigated.

Oh, yes, I’m sure some of them could have. Maybe not Miss Marple, and surely not Nancy Drew or the Hardy Boys, but I would confidently pit Poirot or Holmes or Mason against them.

In fact, I feel sure that some of their careers did include such crimes. The thing is, they’re not very dramatic to read about. So they’re unlikely to have been recorded in the canon.

I mean, Sherlock Holmes slowly investigating embezzlement of funds and giving the reader descriptions of the debits and credits in the accounting ledgers would have made for a very boring set of books.

I bet those literary detectives could do anything if their author allowed them to.

It is a story made to sell books. Of course they were riddled with violent crimes to grip the reader.