I'm sorry, I think your analysis of the cause of the power disparity is wrong. It's not due to numbers.
It's because power disparity is inherent in hierarchical organizations. The CEO is just one person, but their position at the apex of the hierarchy gives them power over everyone else in the organization. Power disparity is baked into the hierarchy—it's not a hierarchy without it.
Unions are a way to balance the power of the employee group against the management hierarchy. Unfortunately unions are also subject to the corruption that accompanies power.
It's because power disparity is inherent in hierarchical organizations. The CEO is just one person, but their position at the apex of the hierarchy gives them power over everyone else in the organization. Power disparity is baked into the hierarchy—it's not a hierarchy without it.
Unions are a way to balance the power of the employee group against the management hierarchy. Unfortunately unions are also subject to the corruption that accompanies power.