For some people, it made their lives better. For most others, it made it far worse
Regime change would have made almost every Iraqi's life better -- except for those who lost employment due to de-Baathification, which was about as justified as the de-Nazification program following WWII -- if not for the insurgency that subsequently arose.
Now, you can argue that we should have foreseen the insurgency. But no one in power, of any political stripe, did.
Think about this little-known fact: prior to the invasion of Iraq, the wargamers' best estimate of how many Americans would die in battles with Saddam's forces was 10,000. This estimate was briefed to the president and Congress. It did not deter Congress from voting for the Authorization for Use of Military Force Against Iraq Resolution of 2002. That's right: 374 members of Congress, including H. Clinton and J. Biden, felt that 10,000 American lives was an acceptable cost for deposing Saddam.
The wargamers apparently gave no thought at all to a possible insurgency, because they did not produce any estimate of how many would be killed by insurgents.
So we now know their crystal ball was quite inaccurate in two ways. Actual American deaths were: ~110 killed in battles with Saddam's forces; ~4,387 killed by insurgents; 4,497 total.
Objectively, one could argue that 4497, being much less than the 10,000 anticipated deaths, is an indicator of a very successful operation. But since the insurgency steadily generated bad news for about 8 years, the political perception was different. And that is why Joe Biden could get away with saying Iraq was the biggest mistake in American history. (That pronouncement was a pure political hack on Biden's part. He could not have possibly forgotten what was objectively a far bigger mistake: Vietnam, where 58,315 Americans were killed, even while we failed to meet the objective of protecting South Vietnam from invasion by the North.)