The 1950s were a good time to be a white American pretty much anywhere, not just New York City. So it’s definitely more complicated than that lol
With less restrictive zoning, more properties and building projects become financially feasible with the banks, builders, and contractors we already have. It costs the government zero money and happens automatically with the stroke of a pen.
It's much more difficult to re-engineer our entire mode of government, taxation, and housing provision than simply removing a few legal restrictions.
Look at Texas - zoning-free, no rent control, and it’s quickly becoming a housing dystopia. Prices are rising rapidly, and as you build out so quickly, your taxes rise as a clip more than twice most places, to build new schools and hire teachers and build roads, etc. and guess what? Private equity firms are snapping up homes at a huge clip, 25% nationally and much higher in Texas, and then rent them out according to algorithms that maximize their profits (in collusion with other landlords using the same software). Why build a Rube Goldberg machine to impact housing prices though the elimination of zoning, when you can affect it directly through rent control and directly incentivizing new construction of cheap units?
That was kind of my point. The burgeoning middle class had nothing to do with rent control laws.
Anyways, most of the research I'm finding contradicts your assertions.
For example, a recent paper [0] about on the housing market in Helsinki found that "new market-rate construction loosens the housing market in middle- and low-income areas even in the short run".
About restrictive zoning _not_ being an issue, a graph from a paper [1] illustrates that Los Angeles is at 92% of its zoned capacity when it had a planned capacity in the 1960s that was more than double what its current actual capacity is. From the paper: "Areas with well-organized homeowner groups dramatically decreased density as a means of controlling population growth, thus directing the future growth of L.A. to predominately low-income, minority communities - communities least able to accommodate that growth due to overcrowded housing, under-performing schools, limited park space and, in many cases, poor transit access. In short, density was directed to the path of least political resistance, a social injustice that exacerbated spatial disparities between communities." The paper asserts that, beyond the racial disparities caused, restrictive zoning has caused rent to become unaffordable and has had a negative environmental impact.
On the topic of rent control generally, one paper [2] estimates that NYC rent controls caused a 20% misallocation of rental units. Another [3] about rent controls in SF found "that landlords whose properties were exogenously covered by rent control reduced their supply of available rental housing by 15%, by either converting to condos/TICs, selling to owner occupied, or redeveloping buildings. This led to a city-wide rent increase of 5.1% and caused $2.9 billion of total loss to renters."
And this general survey [4] found "that economic research quite consistently and predominantly frowns on rent control. [The] findings cover both theoretical and empirical research on many dimensions of the issue, including housing availability, maintenance and housing quality, rental rates, political and administrative costs, and redistribution." In short, “the economics profession has reached a rare consensus: Rent control creates many more problems than it solves.”
[0] https://ideas.repec.org/p/fer/wpaper/146.html
[1] https://i.imgur.com/EIyespr.png from https://escholarship.org/uc/item/6k64g20f#page-1
[2] https://users.nber.org/~luttmer/rentcontrol.pdf
[3] https://econpapers.repec.org/paper/redsed018/918.htm
[4] https://econjwatch.org/File+download/238/2009-01-jenkins-rea...