I have to sack staff to make document assembly profitable

This is not true. If you ask any mathematician to look at any formula, they will tell you there are always two sides to an equation. In the case of profit margins, it is a case of staff time and overheads expended vs. billing amounts; its just another equation. Document assembly can simultaneously lower the left side of this equation (less time spent to produce the same output) and increase the right side of the equation (same staff producing more work output or billing amounts).

An approach taken by one of our clients was to expend considerable amounts in a single area of law, so that the partner of that section was relieved of much of his caseload, allowing him far more time to approach prospective clients for new work. New clients were obtained for the firm based on reduced rates for that area of practice (as document production to complete the matters took a fraction of the time) without increasing staffing levels or reducing the quality of service provided. This area of practice was then used by the firm to get a "foot in the door" with corporate clients to obtain more lucrative work. Not withstanding they make a tidy profit on the "lower end" work, they turned around and automated the higher end work also...

The key to this result was planning for future circumstances. They took me at my word when I said they would need to have a plan for when their support staff got bored with no work, and a plan to either sack their staff or keep them busy. They formed a strategy that worked for them, and reaped the profits.  Higher end document assembly is not too different from a factory in the real world.  The profit margin is higher than manual effort, but the total profit is limited by how many "things" you can push through the factory.  So don't lower staff, increase the amount of matters you push through your system.  Leverage your system more often to claim your margins more often.