Neptunus Rex says, "The reaction on their inner ears should have told them that they were in a rapid descent."
No. Their inner ears can only tell them they accelerated downwards at some point. Once they are in a constant speed drop their inner ears would not sense the drop. They ears might detect something when pressure changed. Ears are tilt and acceleration sensors. They also have pressure on their backs to tell them the nose is pitched up - about the same as the instrument in front of their face tells them the same thing.
Neptunus Rex also says, "Plus, the Captain should have noticed the aircraft deck angle as he walked, or rather climbed, to the cockpit."
That one's a gimme.
Now, just how much of the acceleration into the fall they'd sense is up for grabs if the plane is in violent turbulence.
(Has learned far more about inner ears than she ever intended to learn due to a malfunction in my left ear similar to what the astronaut Alan Shepard had.)