Let's be real: Usually there's a lead actor the investors (money grubbers) want and a lead actor the writers and/or director (storytellers) want. Sometimes the actor is the same person, most of the time they are not.
Indeed.
IN the old days the writer (in Korea the writer sometimes wields a great power on how a series is run) and director had the upper hand. However, with larger budgets needing more investors, the balance of power shifted towards the side of the investors.
In the major stations, the writer/director still have some control, and as a result less money is invested and their dramas tend to become Korea-only.
Red Sleeve was a good example, where a couple of lesser known actors were cast but was shunned by the investors, who needed a better known name for a historical drama . So Junho was cast as the King and the entire script was re-written around him so he gets more exposure. (In the original the court lady was the central character.)
The lead character determines the amount of available budget of a show, which means a lesser known actor can not command enough money which leads to the levels of other actors going down.