In terms of campaign, I don't know a single person who played for it's complexity. If you want a complex 4x title, you play Crusader Kings or Universalis Europa. It's always been about the complicated battles. And the battles have gotten more complex.
And I look at it a different way. Streamlining has improved the gameplay. The settlement system makes it strategic in where you place your stuff. Do you want to make the province a bread farming province or a recruitment settlement? Because it the old titles, it didn't even matter, you could place as many buildings as you want.
Historical authenticity has also increased exponentially. Spartans are no longer wearing Rome. Athenian hoplites no longer use Macedonian Pike formations. No more Elephant Mounted Elephants. Instead of coming from the mummy, the Egytpians are portrayed as accurately looking like their part of Alexander's army.