There's a fair amount of research in economic history on almost exactly this topic. Two recent papers http://www.nber.org/papers/w12328.pdf and https://drive.google.com/file/d/0B4s_WKe-US99LV9XVTNVNzFxYW8... have looked at how measures of the artificial-ness of borders (how straight they are, how often they cut through the territory of ethnic groups, ratio of a country's area to the area of its convex hull) are correlated with various measures of welfare (e.g. GDP/capita, lack of conflict). The papers are often controversial because they often claim something approaching causality (see recent Twitter war https://twitter.com/bill_easterly/status/753252113510268928).
Who are these people discussing on Twitter? Are they the researchers who publish papers on the topic? (I do not mean these same papers you linked to, just asking if they are serious academics.)
Easterly is an economist at NYU (who published one of the earliest papers on the subject), I'm not sure about the others. However the discussion is a good representation of some of the debate that's gone on regarding interpreting correlations between regular-ness of borders and GDP (i.e. is it that having artificial borders was disruptive, or was it that borders were drawn artificially in areas that had fundamental characteristics which have caused them to have lower GDP today).