Rich and Strange Aeons

The names in A:tLA are kind of distinct by nation, but I'm wondering if there are really four sets or just two sets, or two and a half?

Water:
Sokka
Katara
Korra
Varrick
Kuruk
Yakone
Tonraq
Yue
Kya
Lirin

... lots and lots of K sounds, though not universal.

Fire:
Sozin
Azulon
Ozai
Zuko
Azula
Roku
Iroh
Zhau
Ty Lee
Ikem

Lots of Z sounds, a fair number of K ones; made me wonder if there's opposites <-> similarity thing going. Though the sheer frequency of Z is unique to Fire.

Air:
Aang
Gyatso
Yangchen
Kelsang
Jinju

Less obvious pattern, other than lots of nasals.

Earth:
Kyoshi
Bumi
Toph Beifong
Kuvira
Wu
Chin
Suki
Hou-Ting
Kuei
Long Feng

Mixed, but again more nasals. Kind of like Air.