Great article - we saw the same lack of correlation between activity level and weight when analyzing data from 750+ fitness tests:

https://hack.fitness/2017/04/09/what-we-learnt-from-750-fitn...

Increasing activity however does have a positive impact on your fitness (specifically VO2Max) -- the challenge is that this increase in fitness is invisible to most.

That's a big part of the reason why we started Revvo (http://revvo.co) - to make it easy to measure the vital but often invisible elements of fitness.