You have to remember that the other available strategic element was the amount of fuel they carried on the cars at the start of the race, as well as how much they loaded onto the car at each stop.
So even if 2 cars had the same number of stops, fuel adds a second variable (and really a third, considering the different tire compounds).
A car can start heavy or light, and run heavy or light in the successive stints.
I'm not advocating for re-fueling, but rather pointing out that there was more to it, since fuel is a constant in today's state, with all cars beginning the race on their respective full load.