I think you're confusing Deming with statistical process control.

It is true that SPC works best for the non-chaotic parts of product development and manufacturing alike. There are parts of product development that are non-chaotic, and SPC works just fine there, too.

In addition to SPC, Deming had strong opinions on how organisations ought to work and these are relevant also for product development. These are things like

- Understand the underlying customer need.

- The leaders shape the output of the organisation by shaping its processes.

- It is cheaper and faster to build quality and security into the product from the start instead of trying to put it in at the end.

- Close collaboration with suppliers can benefit both parties.

- Have leaders skilled in whatever their direct reports are doing. Use them as coaches normally and as spare workers in times of high demand.

- Collaborate across parts of the organisation instead of throwing things over walls.

- Don't just tell people to do better. Show them how they can do better. Give them the knowledge, tools, and authority they need to do better.

These are just as relevant for product development as for manufacturing. If anything, even more so, thanks to the chaotic nature of product development.