Using 100% brightness makes the test basically invalid. The backlight is one of the biggest power hogs in the whole machine, and the new Macbook is 65% brighter at maximum. That's helpful for e.g. outdoor use, but for office use the proper setting is 150-200 lux (about 50% brightness on the old machines, 30% brightness on the new ones). Testing the machines at different brightness settings is akin to testing them running different workloads.

I'm less concerned with the regression from 2015 to 2016 models, and more with the fact that the Touch Bar model does so much worse than the Function Key model.

At 100% the test might be invalid but I don't think your percentages are correct. I'm sure it's environment specific but I run my new 2016 Macbook Pro w/ Touchbar at about 60% brightness most of the time. At 30%, in office LED lighting, it's way to dark. At 60% it's still darker than a Monoprice gaming monitor that sits right next to it.