Ok so I did a bit of analysis based on current battletomes comparing it to 8th edition (or WHFB) here is the breakdown. (this is not taking into considerations of the 3 battletomes that were released and then replaced.)
WHFB
Chaos - 27%
Order - 47%
Death - 13%
Destruction - 13%
AoS*
Chaos - 35%
Order - 35%
Death - 7%
Destruction - 21%
Not including the new DoK
So if anything Order needs more books, Death needs a little more and Destruction should not see a book for a while, Chaos is almost spot on.
We notice it more in this game that's 2.5 years old than we ever did in WHFB.