This is true for every city. Developers don't really build low-end units. They build high-end units and rely on the age/deterioration of other buildings to eventually turn them into lower-end buildings.
This is sort of working out because people are generally moving back into cities and are willing to pay a premium for it.
The reason why I think this article about Portland is interesting is either their influx of people into the city has slowed/stopped, or they've built so many units that its outpaced the influx. A common narrative in cities is "we're building so many units yet prices are still high!!!" But clearly the equation should be rate of new units coming into the market vs rate of change of city population.
Which also feels like common sense. But maybe its more like, this article is interesting because it shows there's light at the end of the tunnel.