I'm not sure exactly how this relates to the above comment. But you are making the point that the OP made. You need to pair your metric with an opposing one.

I'm not sure exactly how this relates to the above comment. But you are making the point that the OP made. You need to pair your metric with an opposing one. Nobody honest person is going to say "we'll increase time on site by decreasing load time". But on my current project, I've had to take into account that the improved load speed and UX has kept time on site the same. This is actually an improvement as uses are able to interact with the app quicker and therefore their relative active time on site is higher.