Any stability advantage for inner first tents really only applies to those that have continuous deep pole sleeves. like a Quasar or VE25.
If the inner attaches to the poles with clips on tape loops, like a Hubba Hubba, the inner first tent is structurally the same as an outer-first tent that has the inner attached by toggles on tape loops. Such a tent may even be less stable than the equivalent outer-first tent, as external guys won't transfer load to the pole structure so well, just being attached to an outer draped over the top of the poles.
I'm also assuming the Hilleberg ANJAN 2 GT doesn't suffer from the condensation issues that the nallo's and other seem to suffer from in the damp UK climate.
In the interests of lowering your expectations, I should point out that there's no such thing as a tent that doesn't get condensation sometimes. If there's dew on the grass, there will be condensation on your tent - you can't get any better ventilated than nothing.
You've three options:
a) Try to reduce the number of non dewy nights on which you get condensation forming by ventilating the tent well, with features such as a high-cut outer or lots of mesh on the inner. The ultimate well ventilated tent is a tarp. Note that very good ventilation will also let out any warmth you may generate inside the tent, and may let in dampness in the form of spindrift, or even rain if it's very windy.
b) Accept that condensation is inevitable, and try to arrange matters so that it doesn't cause too much of a problem. Look for feature such as a solid inner to fend off drips, or steep sides to encourage condensation to run down rather than dripping onto the inner.
c) Heat the tent so that the outer remains above the ambient air temperature. This is likely to restrict your camping to sites that provide electric hookups.
You can also try to reduce condensation by camping under trees if it's a clear & calm night. This has its own problems, such as sap drips, but you may think them worthwhile.
speaking from distant memory, having owned a Phortess, but not the Ultimate...
They are the same overall design (double sleeved A-pole), the same size, and similar quality.
I think the differences are that the Phortress has plastic rather than bent wire A-connectors, it has a full snow valance all round which the Ultimate doesn't. The Phortress has central ventilation sleeve/tubes at each end, and there are two zips at each end allowing left/centre/right panel opening, The Ultimate has a single central zip at each end. The A-poles on the Phortress may possibly be canted outwards more than on the Ultimate.