I know a very specific use case in management consulting where hours spent by a consultant for a repetitive task (mainly report writing and source data gathering) went from on average of 40 hours to 12 hours per project. It costs the firm roughly ~$150 in token spend to save those 28 hours. They used to be roughly $200/hr (so $5k~$6k).

That's about as hard of data as you can get.

You haven’t shared enough data to tell whether there was a financial payoff for the firm or not. The consultant is a fixed cost to the firm, so saving consultant time doesn’t necessarily translate directly to higher margins nor revenue per worker.

Are the consultants delivering more billable hours per person now?

All sorts of reasons why the answer to that may be: no.