I’d suggest considering why you think scaling fast is a “startup” idea and not just a profitable business tactic.
In my case scaling fast meant bringing on 3-4 subs who could knock out a standardized set of deliverables that I created and trained them on. I did that within a year. I’m sure there are exceptions but I think most consultancies could do this.
So.. then you are back to the startup idea? I don‘t think that works for a lot of consultancies, does it?