Yes, he means the rank progress bar from supergiant to neutron star shown on the user page. Indeed, this can appear a bit strange because it depends a lot on the distribution of other players.
Possible solutions: Make ranks depend on constant whr number thresholds independent of other players. Another possibility that would only weaken the effect is to show a bar for ladder progress from 0 to 100% in the whole player base, not only own precentile. In any case, color scale could be made continous additionally.
To me personally, it doesn't really matter too much which of those measures is taken or if it stays as it is and you just have to be aware that it also depends on others.
Furthermore, I think that the current WHR standard deviation cutoff to translate between real WHR and visible WHR should be increased from 20 to 25.