Both of which share many crucial characteristics with American housing projects, particularly concentration of poverty.

Meanwhile, in the Austrian example given in the link above, Singaporean home subsidization, and other successful cases what you find are schemes that manage to create and maintain an admixture of incomes. There are different ways[1] to accomplish that and they're not all easy, but it does seem like a necessary requirement for success.

[1] As in the Austrian example, you can remove income requirements after move-in, so that people aren't forced out as they move up the income ladder. Or rather than subsidize rent you can subsidize ownership. By having an ownership stake people are incentivized to maintain the property, and even if they move they'll be replaced by someone with a similar income (or at least an income above the initial ceiling). Unfortunately, many liberals who promote subsidized housing scoff at permitting people to continue to benefit from that initial subsidization after their income has increased. But that resistance is precisely the kind of policy dynamic that concentrates poverty!