I wouldn't say they're at threat from AI. Consultancies are most of the time there to partially offload work from the main company, and also to serve as someone to blame when something does not go well. It's rarely about the content itself.
Yup, they are often just Accountability Sinks.
Interestingly they never seem to suffer when they get blamed for their shoddy work. I guess it's free advertising "use us as a third party to blame for terrible decisions and bad data"