Only if your opponent has not read and studied the book.This happens with every army if your opponent doesn't know it.Daemons are ultra customizable - which is cool. But it does create a lot of accounting for the army and demands repeated explanation to your opponents as you change your manifestations. You saying it doesn't (or you haven't) simple isn't true and a silly thing to claim.
In my Meta for the last 8 years almost no one played Daemons. 1 guy from a different city played Daemons who might show up with that army at the tourny.
The result is that NO ONE read the book. No one knew how the army played. Literally knowledge of how the army played would come from watching OnceBittten batreps against Daemons.
Even in T9A, people might glance at the free armybook but unless you are somewhat interested in the army, it's boring to read.
I've read the WoDG book like 3 times and I still find it a boring book to read just because I have almost no interest in the army. I still don't know what the army does. And the 1 guy in my meta who plays WotDG is the same guy who plays Daemons, lol.
Edit: since DL book release I think there are 3 of us who play DL. And a couple hidden Tzeentch players who sold their armies upon destruction of their avoidance shooting army.
Anyway, if you are going to a competitive tourny where people are playing to win, then they should know the enemy books. Or at least be very familiar with the common builds.
I play 10 Games with Myrmidons. Each time, for craps and giggles, I change the manifestations on the unit. Then I add in Omen, or Kuulima's, or Herald, THEN I state the Dominant from General - that will be different in every single one of those 10 games, but my opponent is still looking at 20 Myrmidons. See what I mean?
Even if you're AWARE of the options of each unit, and if you have that memorized then hats off to you, it doesn't matter as you're explaining every single game as it's different. It's not the same as saying "This unit has banner of '"his" , and this dude gives them hatred = as that's pretty much what it can/would always have.
Maybe I'm not explaining myself properly (wife tells me this all the time, lol) And I'm sure not looking for an arm wrestle, just stating that Daemons are obviously more confusing than any other armies because of the amount of options, multiplied by the number of influences the characters can give.
I play Daemons A LOT, home games, tournies, whatever and I can get almost sheepish from my opponents reactions to all the things I have to explain, and I simply won't believe that another individual NEVER has to do that.