Me : Necessary evil to get people started with mapping, hence "scaffolding". It helps people frame a problem. Over time, with experience, you'll find the Y axis problematic ... which is when you should drop it.
Ordering by value means the kettle is a really high level part of the chain precisely because it's expensive.
Me : Perfectly fine. I've just found it easier to discuss a chain growing upwards like a tree with the roots at the bottom and the canopy of what you see at the top.