I think the y-axis (polarisation) is pretty good and it feels correct, but the x-axis (entrenchedness) seems to be quite random, and an unjustified amount of importance is given to it. Like the US and Brazil are obviously super divided; aided by a centuries long two-party system. This is a huge problem and there seem to be no clear solutions for it.

Compare that to Sweden and the Netherlands that have representative parliamentary democracies and well functioning institutions; but this graph somehow classifies them as equally bad.