^^^^
I agree when you compare the Mk5 with the Mk1 or 2 but the evolution is Mk1 > 2 > 3 > 4 > 5 > 6 and the Mk5 evolves well from the Mk4 even if the Mk6 does so even closer.
It's all rather academic anyway. I've driven the Mk6 and was very disappointed as I expected it to be a significant leap ahead. My dislike of its styling, especially its interior, is purely subjective. As I wrote in my review of the Mk6 it's very much not for me but that doesn't make it rubbish. I quite like the Golf R though.