Good points for either argument. However, I'm still a "student of the neck as a connector theory" rather than a separator for reasons you already mentioned (i.e. both hulls are dependent upon each other). Actually, I see the saucer as more dependent on the engineering hull for survival since power generation and life support is provided by the engineering hull. In the event of separation, the saucer can sustain itself for awhile, but, all by itself, without contact with starfleet or a starbase, it's nothing more than a lifeboat living on borrowed time. Power will be exhausted, and it would take you forever to make any headway traveling at impulse speed.
In this respect, the neck can be seen as an "umbilical cord" (if you will) for the saucer.
"We don't know if the shaft is vertical - an angled one would probably make more sense. Where does the evidence for a vertical ladderway (higher than two decks tall, anyway) come from?
Without power, or a tubolift malfunction, there must an alternate way to get from one hull to the other. (Refer to Scotty and his "lads" using the ladder to climb down to engineering in the "Doomsday Machine.")
Hmmm...the idea of an angled turbolift is interesting. In most fan-inspired cutaways, the only turbolift path I've seen drawn out in the neck is straight across to the back and straight down. I've even seen a stairway that parallels the back end of the neck.