Lol. At what cost elsewhere in the absence of the steels? Mauling large section timbers is no fun and is time consuming (costly) in itself. Couple that with wall plate (eaves) issues and it become more than just head scratching. However, the worst offence with deeper section rafters is the timbers themselves misbehaving, especially when patterning. That's before getting started on large section hip blades which are difficult enough when moderate size.
I disagree with your rationale that it is a steel cost saving.