I do my homework on this stuff.
The hull of starfleet ships tends to be somewhat thin. Look at any window; the hull tends to be less than a foot thick.Are you saying that the hull of this ship is like the body of a car? Just the "metal" skin, not structure?
And structural beams inside the hull are routinely within the rooms as part of them, in TOS and TNG. See below :
Dude... there's a picture of it right there. You can SEE it. Choose not to believe it, if you wish. I really can't do much more to convince you.There is no way there are 4 decks in the saucer. 3 decks (plus bridge)