You have it exactly right.
If wealthy elites are going to spend a BILLION dollars on manipulating elections, why bother with elections. Have small controlled caucuses. It’s much more time effective and cost effective to these folks and then they won’t have to worry about the popular vote not reflecting the delegate votes.
BUY DELEGATES.
Why waste hundreds of millions on ineffective advertising?
Just buy the delegate. Everyone has their price. Congress has proven this.
The advertising has to be done. The intended outcome is that the public believes it participated in a meaningful, unrigged, honest, election. If the process of electing the government looks rigged, if it doesn't include the appearance of persuading the public, the public will not attach legitimacy to the elected government. So the elites spend a bunch of money to propagate advertisements, in order to create a perception that public persuasion is necessary in advance, as if the choice at the ballot box makes a difference to the ruling class. Rigging the ballot box or buying delegates is sometimes but not always necessary to prevent a candidate that is unacceptable to the ruling class from getting into elected office.