when every new building requires effectively bring special interest groups, politicians, regulatory boards, and unions, their due is it a surprise cities are not getting better.
they are serving a politically connected elite, not the people who live there or want to live there.
Los Angeles is low-density partly because it spends lots of land on roads and parking lots. It needs lots of roads and parking lots because everyone drives. And everyone drives because the city is low density.
Cars, also, not really that big of a problem in themselves. Commuting is the problem. This is a symptom of depressed wages; people are willing to spend extra time (commute) in place of extra money (rent).
It is a self reinforcing vicious cycle. You can break it anywhere. I recommend started with breaking zoning because it is least painful. If you eliminate cars people who currently depend on cars will be in trouble since they cannot live their life. Eliminate the need far cars is a much slower thing that won't have any noticeable affect for 20 years, but it is a much less painful transition.
First step is to eliminate eminent domain. More infrastructure only begets more people using said infrastructure. When the many can't take from the few, they might actually have to give up some of their luxuries to have what they want (eg, a place to work).
As someone who has, in the past, been a neighbor to an unofficial junkyard (unzoned land), and as a person who currently only has houses for neighbors (zoned) thank god people can't do whatever they want.
A better method is what they have in Japan, where local government has almost no power at all to control how land is used.