Interesting stuff! It's good to see a car maker tailor their suspension for a specific market, unlike the Germans who fit the same granite like springs and dampers for every country.
Suspension and engine calibration are the 2 areas that take the longest to develop, sometimes years. And then we go and throw all that good work in the bin and fit aftermarket stuff
Something to bear in mind with the MK5 GTI is how old it is now. Suspension technology has come a long way in 12 years. Some of the aftermarket kits out there are really good, and there are some I wouldn't fit to my wheel barrow, let alone a car. The GTI is a low car to begin with - and I'm not talking about scene arch gaps - so doesn't have masses of suspension travel from the factory. Lowering it can have a worse affect on the handling than predicted. My VWR kit is only -15mm but I've bottomed it out several times already, with one passenger! How people manage with coilovers dropped -50mm or more, I have no idea.