Zoning does that too. Usually MF is designed as a buffer between commercial and single family (as proxy for more/less affluence). Without zoning, it just happens more naturally because the commercial is going to usually want to be on a major road, then land next to busy commercial is not desirable for single family housing so a MF developer will build there.
The part I liked about it was the city was able to adapt to change. I saw the inner-loop part of Houston as a hellscape as a kid. Then ~2000s when inner-city gentrification began, it went quick. Neighborhoods tend to support more local business than the big box strip centers that proliferate in the master planned world. Also, master plans are just copy&pasted every couple of miles so it all just looks the same[0]. I liked having neighborhood restaurants and other quirky stuff inside an old house in the neighborhood, you actually knew the owner and it facilitated a sense of community. It's rarely ever actually in the neighborhood, just on a main thoroughfare that pretty much is high traffic regardless of the business use. I see living on a high traffic road not very different than living next to a busy shopping center.
The other thing I've noticed now that I live in Dallas (which is pretty similar to Houston except with zoning). I frequently see an undeveloped parcel of land and I think, "wow a X shop would do well in this location." I look up zoning and it's not allowed. What is allowed, IMO, wouldn't do well in that location. That's why it's still undeveloped land. Some map drawn 50+ years ago probably made some bad assumptions. Typically the neighbors will fight any zoning change because they actually like that nice undeveloped lot next door. Developers with bigger pockets pay the neighbors off so they don't fight the zoning change.
Hard to explain, but Dallas is known for 'lack of culture' and having lived in other Texas cities prior (Houston and Austin) I think it's largely due to with how it was designed. It's difficult to build anything unique or artistic here. Until it was banned a couple years ago, many of the city's in the metroplex building code would mandate exactly what brand and color of brick you could use. So we have entire small cities in the metroplex that are red brick (it was a trend in the 90s when that area was being swallowed by sprawl, and it's exactly what's off trend the last decade+) Actually, most cities still mandate it and if you're a developer you'd have to file a lawsuit to get your non-conforming design permitted (you'd win because State of Texas banned this a few years ago, but many municipalities have conveniently not updated their building codes).
Which segues to this;
> If you lack that financial security, you may be stuck next to all sorts of undesirable properties
But at least your in the mix of the city and somewhat able to interact and have social mobility, access to the core business districts and jobs that service the higher income citizens. In Dallas, the economic core/center of gravity is moving north towards Plano and those lacking financial security get pushed further and further south (usually). This essentially is a ghetto, food desert, high crime yet over policed, etc and provides little access to social mobility. It also reinforces a lot of the race issues that exist in our country. Dallas is very segregated compared to Houston.
[0] Most of Houston is very guilty of this, most of it also has defacto zoning by another name. I forget what it is, ordinances on noise and traffic impact or something. The inner loop area is pretty organic and sense it's well developed, you pretty much know who your neighbor is going to be. If you buy a house next to an undeveloped lot, you're rolling the dice, but there's likely not any lots big enough to build an oil refinery or a shopping mall or whatever. If you're in a residential area, it's likely a small lot and will eventually be built as residential.