In all of these years, I have never even considered her to be the ruler/leader/President of Vulcan. I thought she was some type of ritualistic/spiritual leader and important in terms of Sarek's circle of influence. I assumed the "all of Vulcan" comment was concerning her personality, control, etc, that she embodies all of the stereotypes / heart and soul of Vulcan culture in one package.
I never even thought of that. Instead of being a big wheel in politics, T'Pau could have been more like Jerry Falwell and Joel Osteen. She could be the pastor of a megachurch with huge reach and influence in society. But it's not really a church, and the "religion" is Vulcan logic.