"Kay said the US was wrong and this vindicated the UN."
Kay said "we" were wrong about stockpiles of WMDs.
He said there was evidence of Saddam withholding evidence regarding WMD programs which he should have revealed.

You are also not allowing another possiblity. If the French had not said it would veto, it's possible that Saddam might have chosen a different path. It's also possible that without this threat of a French veto, the coalition might have delayed invasion. But French refused this option under any condition. Therefore, from the coalition viewpoint they had already wasted time which could have been much easier conditions for ground forces- no heat and no sandstorms. And the window to start before the summer was rapidly disappearing. And keeping +100,000 troops near the border of Iraq for months, risked soldiers lives, and cost billions of dollars, and affect their combat readiness. Meanwhile, the French govt plan was to delay as long as possible & therefore resulting in costing the US billions of additional dollars and increasing the risk to soldiers lives.