Iran-Iraq War and Post-Gulf War 1 sanctions were each worse for Iraq than the 2003 invasion (by far). The various problems with the occupation (which mostly fall on Bremer/CPA and GWB/Cheney) were probably within an order of magnitude of Iran-Iraq and sanctions, maybe even directly comparable. Rise of ISIS (also a separate thing) and general sectarian violence as also bad at that level.
It's hard to tell how far back the causality chain you should go. A simple "kill Saddam, put any reasonable other person in, don't extensively reconstruct the government, GTFO" was what I was assuming would happen in 2003, which probably would have been net-positive for Iraqis. If you are bundling "invasion in 2003" with CPA + sectarianism + ISIS, then they're collectively highly net-negative for Iraqis, but I don't think they were necessarily linked in 2003.
I still would have opposed it as a US person (because it was a distraction from Afghanistan, which ALSO should have been concluded in late 2001 vs turned into a 20 year quagmire...)
Colin Powell has a decent place in my memory for his work in the 1990s and before, but he definitely spent his reputational capital in lying to UN, even if it didn't ultimately influence the course of action. I could certainly agree with him perhaps even overdrawing that account in total.