> The core insight (that “light bulb” moment) of Strong Towns for me was that low density suburban living requires more roads, curbs, sidewalks, and pipes than it pays for in tax revenue—meaning, it’s not solvent.

I mean, whether or not that's true is a question of tax rates, and probably also a question of whether you are counting only property taxes paid by residents or other revenues driven by their presence of the housing, including those from businesses enabled by having housing that is attractive to the demographic that prefers suburban cul-de-sac style housing.

> If a cul-de-sac is stripped to its essentials and brought to the bar of the balance sheet, it has nowhere to escape....It exists for one purpose and one purpose only: to provide access to the homes built around it.

Incorrect. Cul-de-sacs, and non-grid suburban road designs more generally, exist to deter access to the homes built around them. Specifically, to deter non-resident access to and traffic, especially high-speed traffic, near them. There are a wide number of reasons, but promoting pedestrian (and particularly child) traffic safety, deterring crime, and reducing noise pollution are among the reasons.

> e.g., roads are assumed to have an average lifespan of 14 years according to our local Engineering Division

But are cul-de-sacs assumed to have that average life? The life of a road depends on wear, which depends on traffic volume, traffic speed, and vehicle weight (immensely!). Cul-de-sacs are designed to minimize all three compared to through roads, and thus should have much higher than average life for the broader class of all roads.