Urban planning: The built environment

these compromises in the interests of cost reduction do not seem like a good choice

Not OP, but there's more going on here than cost, and I think it's worth a discussion.

A lot of the urbanist crowd want single-stair multi-family units for reasons well beyond cost, although keeping housing affordable is still a legitimate goal. Michael Eliason, who was quoted in OP's linked article, did a piece in Treehugger about single-stair buildings a couple years ago, and he identified some of the down-sides of the American "double loaded corridor" format that is necessitated by having to have two stairwells:

Double loaded corridors prevent units from getting lights from multiple sides, and they don’t allow cross ventilation, which is a growing issue on a warming planet. (Yes, even for multifamily passivhaus projects.)

Double loaded corridors generally have dark hallways, and result in less usable space per floor than a single stair configuration, especially if your building code allows units to enter directly off the stairwell, as they do in Germany, Austria, and France. There are also structural tradeoffs with a double-loaded corridor, particularly for a building that is cellular or repetitive in design like a hotel, dormitory, or efficiency units. Single stair buildings generally have more flexibility in their floor plan configurations.

Another issue with large double-loaded corridor buildings is there are more people using the same elevators, halls, and entries. There are more people entering this sort of building than would in a single-stair configuration, due to limits on the number of units per floor. There are certainly social implications for this worth evaluating, whether one is more personal or impersonal. Post-pandemic, does it make sense to design buildings where many residents are using the same public spaces or does it make sense to partition buildings into smaller pods?

Similarly, Henry Grabar did a piece in Salon about single-stair apartment buildings that focused on the social experience of living in a single-stair building versus a hotel-style double-stair building split by a long hallway:

Another Floor Plan Twitter fan is Conrad Speckert, an architecture student at McGill University who takes that required second staircase personally. “I grew up in a three-storey, single egress apartment building where we knew our neighbours well, the stair landings were generous and naturally lit, and everyone got pretty crazy with their Christmas decorations,” he writes on the website for his master’s degree project, Second Egress. “My childhood home in Switzerland reminds me that stairs should be about more than just circulation and fire safety, and that there is a sensuality to them too—the tactile sensation of a winding guardrail, the slip-resistance of the treads, the wash of light from a skylight or the breeze from an operable window.”

Speckert pointed out that in countries where single-stairs are permitted, many of the units have doors that open directly into the stair, which allows the designer to bring natural light into the stairwell to illuminate everyone's door, and it encourages small interactions with neighbors that builds community.

“There’s an intuition that once a building is more than two stories of height, you use the elevator,” Speckert told me. “But when you have a building with one stair that opens directly to the landing, you have the opportunity to design that stair. To not make it concrete with an aluminum guardrail. Now you’re sharing circulation with neighbors, you may know them.”

In terms of safety, the Treehugger piece mentioned that balconies are used as second means of egress in many European building codes, and they have emergency systems to exit via the balconies in an emergency. Even though most of those European buildings don't have sprinklers, their fire loss rates are lower than in the U.S.

And to come back to cost, I'd argue that it's fair to think about cost, particular as efficient mid-rise housing is likely to be one of the primary housing formats for densifying the urban landscape of most American cities. We're still in the middle of a housing crisis, and it's worthwhile to look at how more and better quality housing can be built for less money, whether that's re-examining stairwells, or parking mandates, or developing efficient prefab practices. The Salon piece quoted a developer from Philadelphia who thinks single-stair is key to building smaller in-fill multi-familiy buildings rather than massive, soulless apartment buildings.

Bobby Fijan, a developer in Philadelphia, is another guy who likes a single stair. Fijan calls himself the Bill James of floor plans, a reference to the baseball analyst whose keen statistical-appraisal technique helped changed the way players and skills were valued in the sport. “I’m not sure the effect it would have on a 250-unit building by Mill Creek,” he said, citing a large apartment developer. “But it would be particularly meaningful on urban infill”—the one-off apartment projects taken on by developers in already dense neighborhoods.

I'm not an architect or engineer, but I've lived in my share of apartment buildings, and I'll say that I'm somewhat sympathetic to the single-stair advocates. The long-hallway, hotel-style apartment buildings suck to live in. They're soulless, the hallways are dark, it's hard to meet your neighbors, and unless you're lucky enough or pay enough of a premium to get a corner unit, the apartments are dark too. They're just not nice to live in, whereas a lot of the European flats you see in these articles are more attractive and would make for better community-building, and that's worth something too.