There's more to strength than eyes

Okay, I accept that point. However the main point I wanted to make is that a mistake usually not only leads you to lose points locally but also leads you to lose strength. If the mistake would only lead to the local loss of points than I would speak about linear development. The fact that you however also get strength when you are making points (especially through actions such as capturing stones) suggests to me that the effect is larger than linear.

What level are you?

As written above I'm 1 kyu in Germany. At least that was my ranking when I played regularly two years ago.