Isaac Blue is no softer than any other colour in the palette
Agree, solid and metallic / pearlescent coloured cars will all have primer, base coat and lacquer and go through the same painting process so the ‘hardness’ should be the same irrespective of the colour. Begs the question why VW charges more for metallic paint over a solid paint. The exception may be pearlescent Oryx White, which has an extra stage in the painting process - a separate pearlescent layer applied to a Pure White base coat before the lacquer coat is applied. Assume this extra stage in the painting process is the reason for the significantly higher cost of Oryx White paint.
VW paint always used to have a reputation for being hard. Maybe modern water based paints mean this is no longer the case, although I’ve machine polished the last two VW’s I’ve owned - both with water based paint - and would say that the paint does seem quite hard. Maybe on a brand new car the paint hasn’t fully cured when the car leaves the factory, but it continues to harden more over time.
Soft paint on Golfs is normally found on anything that is painted in gloss black, so on the R it's all the bumper/window trims, mirror caps etc.
Pretty certain that the piano black B pillar trims are a gloss black plastic and not actually painted. Whatever the finish is, they are very soft and very prone to swirling.