Sistani and Muqtada are examples of powerful Shiite clerics who wanted to limit Iran's influence on Iraq. From a political perspective, I say that these two gentlemen were at least sincere to their country. In the very early days of the American occupation, they mobilized massive support which obstructed the American agenda of transforming Iraq into a Western liberal and secular democracy that would be a natural ally of Israel. The Americans even wanted this to be Iraq's new flag:
(https://fotw.info/images/i/iq!2004.gif)
In the very early days of the American occupation, the so-called "insurgency" to liberate Iraq from America was non-sectarian. Sunna and Shia co-operated for the common Islamic cause of cleansing their land of non-Muslim foreign occupation. Having said that, it was of course a positive development that the Americans removed Saddam from Iraq. The Americans did it for their own narrow self-interests (which is why they did not directly invade and liberate Syria from Baathist rule - the cost of doing so would outweigh the interest for them). The Muslim Brotherhood in Iraq initially joined the Governing Council. Tragically, al-Qaeda came in and under Zarqawi sparked a sectarian civil war which proved to be a disaster for the Sunnis. They were ethnically cleansed from Baghdad and elsewhere and subjected to the terror of Shiite death squads in revenge for the Samarra shrine bombings. Otherwise, it was a great opportunity for the Sunni Arabs to advance their own Islamization project as the Shiites were doing under the leadership of Dawa party, Muqtada, and SCIRI (al-Hakims).