I expect it to be 50 %
The part of the quote I was referring to is: the effects the output profile has on the image cannot be seen in the preview.
Does this not mean that any change happens at the moment of export (output profile) and not on the screen (preview) ?
I appreciate your patience by the way @heckflosse 
I admit my ignorance: I might be completely out of track, but I’d like to understand it once for all.