Citizens vote for reps but parties run by their own rules. Both divide the spoils and compete for the upper hand. Since parties are fed both by voters and power brokers, they have an edge over voters. But we still have two different life forms, as it were, inhabiting the body politic. I don't like it. Parties have an internal voter structure and since motivated voters from the general population can join that, the potential for outrage is defused.
The party system captures the democratic spirit and allows insiders and hacks to turn Representatives of the public will into Representatives of the party will. The leader of the party has the greatest ability to steer the party but this CEO is unelected in a sense because no one but his own riding voters get to advance him to the leadership. Leaders of each party have made news in recent years for trying to rig nomination meetings. So there you have it, two different life forms feeding on the body politic. The party gets more food than the registered voter.
A parallel occurs to me: In our own bodies, there are at least two operating systems. One is simple animal behaviour to feed and reproduce and the other is like an uploaded software called "me" that cohabits and does its own fascinating things most of the time. "Me" has the upper hand. Craziness occurs when both engage in the same activity. This leads to all the comical things that men and women do that don't quite make sense but we all understand.