< your abilities don't scale

True, but making a good process to replicate it further can scale

I speak from experience - you can leverage the cooperation of 3-4 successful consultants to fill gaps or land larger projects, but you'll make more money consulting than you ever will trying to make your process scale.

The only exception is if you target a repeatable market for business processes.

Why does this have to be? If you pay the good consultants what they are worth, and then pass on the cost of them + an appropriate cost for leading the project(s) + your consulting fee for working within the project, you should make more than consulting alone, no?

That is patently untrue. Otherwise, agencies wouldn't exist.

In my experience and close friends, the agencies hire consultants to do the difficult work, and are not good at managing that more difficult work.

Agencies have no understanding of how to estimate a software project, and arbitrage underpaying moderately skilled workers who don't know any better working 50-60 hour weeks to compensate for bad schedules and lowballed estimates. I've never worked at an agency where a 40 hour week was remotely the norm.