I'm aware of that, but the proportion of overhead varies per company. Six months seems like a long time for a ventilation system, and the point being made in this thread is that the runway available for some spun-off group of former Boeing engineers would need to accommodate the very long schedules of the design stage.

I'm just curious how much inflation there is in those schedules because I'm sure it's not zero.

But you make a good point that these long runways are because the overarching tradeoff is one that prefers taking as long as it takes.