Some investment firms already seem to be able to grow revenues without growing the number of employees.
Growing revenue without growing employees is probably a good thing for many reasons if it's possible. However w/r/t the investment firms, imo many investment firms can grow revenue without hiring only when the bottleneck constraint on their revenue is just their reputation.
As their reputation grows, investment firms are often able to do the same thing but with a larger quantity of investor money. Perhaps their reputation also helps on the other end; maybe some can make the same quantity of deals per unit time but as their reputation grows perhaps they become better connected so maybe the deals get bigger and/or more profitable.
In other industries you have to produce a higher quantity of goods or services in order to get more revenue, so this may not generalize.