AndreasT,

I think you don't have misconceptions.

When you expose a test strip, even if you set aside the whole concept of speed, you can always get a measure of the contrast.

Photographers could work from box speed, if they used appropriate metering technique (like incident metering). But people meter badly at times. I remember times when I got underexposed shots using the camera on automatic because I included too much sky or backlit situations.