If all you want is an opinion, in my judgment the answer is none of the Atomic regulators models justify their higher price over the Z2. However, I suspect you were hoping for a little more reasoning than that.
I needed a regulator rated for reliable operation at 300 Bar/4,351 PSI supply pressures and the Atomic and Aqualung/Apex were the only ones I could get the manufacturers to verify it is clearly in the Atomic literature. Breathing performance-wise, there is no difference in any of the Atomic regulars.
If you look at Atomic's Web site, it is difficult to find any differences between their models beyond the swivels you mentioned and materials. In my view, a first stage swivel is a negative. Any dynamic O-ring seal is inherently less reliable than a static seal. No extra O-ring seal is even better. I do have a much older similar flow-through balanced first stage with a swivel and fail to see the utility. You already discounted the value of the second stage hose swivel. Your personal ergonomic preferences may be different, but if they were that useful all regulators would have them.
Atomic Aquatics Regulator Specifications
Atomic Aquatics Regulator Systems Comparison Chart
As far as materials, the price for lighter weight TX2 would take a very long time to justify in baggage overweight fees. I cant see why a non-traveling divers would care since it only shifts weight from the regulator to lead.
There is a logical argument for materials with greater salt-water corrosion resistance, but I have not seen enough parts that required replacement due to corrosion on other brands over many years to justify the additional purchase cost. Even first stages used by commercial saturation divers on their bail-out bottles would not pay for themselves based on reduced reliability or maintenance costs.
In the case of the B2, the 24 Grams/.84 Oz (373g - 349g) of weight saved by using Titanium in the second stage body couldn't possibly reduce jaw fatigue enough to matter.
None of this is intended to demean Atomic as their quality control is second to none; their regulators are very intelligently designed, craftsmanship is excellent, consistently have among the very highest simulator tests, and appear to stand by their warranty. We can debate the utility of simulator scores above other regulators, but it has value in the form of reassurance to many people.
Atomic will perform factory service if you do not intend to service the regulator yourself and do not have full confidence in the service your dive shop provides. They are also the only company that I am aware of that puts all of their production regulators though an Ansti breathing machine test cycle, which tests the regulator at multiple depths rather than just on the bench.
Atomic Aquatics Manufacturing - Putting It All Together