That's because the MK5 GTI was crap. MK7/MK7.5 chassis was a leap frog moment for VW. It's like the difference between the GM Alpha chassis and everything before it. Light years difference.
I had a MK6 Golf R. I now have a MK7 GTI and a MK7.5 Golf Alltrack and the Alltrack handles better than...
Looks like the 275/35/18 V730's are back in stock at Simpletire: https://simpletire.com/brands/kumho-tires/ecsta-v730#v=1&tireSize=275-35r-18&mpn=2284013&pageSource=brand&itemId=213173&delivery=Del3&curationSource=none&productPos=1&rad=EE