I agree that people probably overestimate the role of oil, but you have to keep in mind that the current world paradigm is not the world paradigm at the time of the Iraq war, and that there are very personal issues involving the Bush dynasty and its connections with the intelligence-executive infrastructure at play as well.
The US shale oil issue has also really flipped the script as well; it's something I don't think anyone was predicting at the time. The rapidity of solar and wind's rise is another surprising thing.
I don't mean anything conspiratorial about that. I just mean that, yes, China is dominant now, and there's a certain global socioeconomic-political dynamic. But at the time leading up to the Iraq war, the world was a very different place in terms of global politics and energy economics.
It is probably more fruitful to argue over whether or not the US government anticipated these geopolitical changes well enough. But to point to things that happened later as a rationale for what transpired before seems backward to me.
In some ways, the transition we've witnessed is from a oil-cold-war dynamic involving the US and Russia/USSR to a vacuum, made by renewable energy and Asian and European economic growth. As an American, I feel like we should sidestep issues about Euro-Asian supremacy and American-Russian decline, and take a hard look at what assumptions we often make, and what it increasingly looks like is that many of the old political blocs are starting to seem irrelevant to a prosperous future. I think America has a dominant role it can play, and will, if it just starts being forward-looking instead of backward-looking.