I disagree with you- and the critics- about Rumsfeld.
The US military- with Rumsfeld in charge-could have successfully accomplished any mission ordered. Where given carte blanche, to topple Saddam, the military performed magnificently.
If Rumsfeld would have been found incompetent we will never know.
What occurred was a loss of political will from the White House under pressure from State and their UN, EU, etc allies.
The military - including its civilian leadership- just takes orders from the "Decider". And the orders were not to do what it takes to "win".
I agree with you on the main reason.
Our military's hands are tied up by the what-are-people-going-to-say fear.
Our military was and is not allowed to conduct the war against the insurgency and their Iranian allies the way they are capable of.