I absolutely agree that there should be stairs... I had assumed that the only access to the outer ring of deck 6 was via stairs or ladders down from deck 5.
As for the turbolift arrangement, it is hard to get a complete view of this without taking other decks into account. So here is a very rough sketch of decks 1 through 6 to help illustrate what I was thinking on this subject.
The loop on deck 5 was only left in place originally because I only planned on it existing on that deck. The idea of too many of those types of loops cutting off the core of the primary hull seemed odd. I figured one would work just fine. Also, I haven't put any thought into what would exist on the other decks, so I either omitted corridor and room spaces or left something similar to deck 5's arrangement.