3 ideas
The size of a role is measured by the longest task the incumbent is accountable for completing without review, its target-completion time. This objective yardstick replaces subjective judgments of a job's importance.
Organizations naturally sort into discrete strata (roughly at 3 months, 1, 2, 5, 10, 20, 50 years of time-span) reflecting jumps in cognitive complexity. A requisite structure has exactly one managerial layer per stratum, no more.
For accountability to work, a real manager must operate at the next-higher level of complexity than the subordinate, able to add value to their work. Too many or too few layers produces confusion and disengagement.