Oh, I understand my mistake now - I was envisioning spot-type lights rather than wide bands in the shaft.
Yes, a system with larger trunk lines and smaller branches makes sense. But aboard a starship, space would be at a premium, so the extent to which the large "spine" helped might be limited. Rather, traffic loads might be handled chiefly by using one-way lanes in a multiply redundant network - say, the lifts would circle the saucer clockwise at a certain radius, counterclockwise at another.
The ST5:TFF vertical shaft I could easily see as a "grand trunk" going up the spine, with the top end somewhere near the impulse engines and the bottom at the cargo levels. Perhaps not a turboshaft as such, but rather a generic utility lane that accommodates lifts but also various other kinds of hovercart or container.
But it could also simply be an empty space left by the refit that replaced the TMP-style thin vertical warp core with the thicker thing seen in ST6:TUC, with the actual turboshaft being elsewhere. After all, this shaft we see has no doors for any of the in-between levels, making it pretty useless for moving personnel, and doesn't really show any turbolift-compatible side branches for the top and bottom levels, either.