Bjergsen's Azir rune page

Hey guys. I really love Azir and naturally I decided to check probuilds.net to see if they had though of something I hadn't. I was curious about Bjergsen because I noticed he build Athene's without any additional cdr, which seemed very strange to me. Looking at his rune page, I realized that he got the last 15% (after sorcery mastery) from scaling cdr blues.

Anyway, I thought this was interesting and was hoping to see how it was working for others. I don't own scaling cdr runes and while I'm working on that I'm hoping to get feedback from others.

Sources:Bjergsen http://www.probuilds.net/guide/NA/1572929054/49159160 http://www.probuilds.net/guide/NA/1574602653/49159160

Thanks for reading.