You're correct, they are advocating that stroads be removed. The difference is that in your comparison to computers you assume that roads, like computers, have a quasi-linear trade-off between performance and power (ie: alpha x performance - beta x power = 0, obviously a simplification, but I hope it gets my point across) and thus a middle-ground between the extremes represents a good compromise for a variety of applications.

Strong Towns appears to be arguing that the trade-off between movement (roads) and value (streets) is highly non-linear, and that the middle-ground's combined performance is so much worse than either a street or road that it's not worth building. See the comment below about counter-tops vs. stoves for an example of an extreme binary case.