Kevin, thanks for the feedback! Your suggestion to look at times rather than Watts is a good one, because it comes at the problem from another angle. Unfortunately, the time data for such a comparison should have units of seconds because minute-level precision would not be sufficiently accurate. The device timeline only displays data rounded to the whole minute, as shown below.
A couple months ago I created a wish-list item which would include second-level data on the device timeline. I can come back to your idea if the developers ever implement that feature!