The only aspect of the battle that could be considered 'unexpected' was the massive use of Kamikazes against the fleet, although the battle of Lingayen Gulf in the Philippines gave the allies a taste.
As for whether one thing isn't like another:
Guadalcanal - 7k casulties. 2060 sq miles 36200 defemders
Tarawa - 1.7k casualties approx 1 sq mile 2619 defenders
Saipan - 13.7k casualties 45.5 sq miles 31000 defenders
Peleliu - 9.7k casualties 5 sq miles 11000 defenders
Iwo Jima - 28k casualties 8 sq miles 22000 defenders
Okinawa - 84k casulties. 463 sq miles 120000 defenders
Oki was fought in the lower third of the island where the bulk of the Japs and their prepared defenses lay. After Iwo, the allies knew what was in store for them ashore.
I’d buy that. Estimates before Iwo Jima were very optimistic. Arguing that ‘Americans had learned their lesson before Iwo Jima, don’t jive with the American estimations of casulties before the battle.