I think this is one of those things that you don't "solve" and it's done. You might be right that things tend to centralize, that's why there is a need for some force to break things apart once the players become too powerful. Maybe it's regulation, maybe it's competition, maybe is people being loud enough (probably not...)

Just like democracy, you are never "done". "Oh great we are in a democracy nothing can remove that from us!" nope, gotta fight to keep it that way...