Regardless of what the healthy ratio is, managers are typically incentivized to add more managers between themselves and their reports. This creates the illusio

Regardless of what the healthy ratio is, managers are typically incentivized to add more managers between themselves and their reports. This creates the illusion that they are more senior and worth of a promotion to senior manager, director, VP, etc. so even if your company has a healthy ratio, there needs to be a force counteracting the natural desire of managers to grow their ranks.