A perfectly optimised set of routes can be deeply unfair, and an unfair schedule does not survive contact with a team.
Why it matters
Pure distance optimisation will happily give one technician eleven tight stops and another five scattered ones, because that is what minimises total miles. The second technician is not slower; they were handed a different problem. Over months, the imbalance reads as performance difference and gets managed as one.
Balance is also what makes a schedule predictable enough to plan around. A team that knows roughly when it finishes can be staffed, trained and relied on.
How you notice it slipping
The spread between the earliest and latest finisher is wide and stable. The same people always carry the heavy days. Overtime is concentrated rather than shared, which usually means the plan, not the person, chose it.
What to do
Decide explicitly what you are balancing: hours, stops, or revenue. They are not the same and optimising one will tilt the others. Then look at the spread each week, not the average. The average is always fine; the spread is where the problem lives.