From that I conclude that you've probably never done A/B testing and discovered how difficult those deltas are to accurately measure, or discovered how changes

From that I conclude that you've probably never done A/B testing and discovered how difficult those deltas are to accurately measure, or discovered how changes upstream waterfall down through your site We've done it before. We've launched new screens, measured the usage, then done a bunch of changes to the screen and seen usage go up. We also have a lot of good data on which screens generate the support call, data on the conversions of all the different screens, etc. But again, your points are all good. We have pretty good data. But it's nowhere near as simple and clear as the same type of measurement for a sales person. Would the data be good enough to base pay on? I don't know.