Yeah the AR8 is their top of the line model (besides the razorback). In comparison to the Solovairs, the AR8 is basically twice as thick - it is a fully leather lined boot, two layers of leather everywhere... Besides that, it has a third reinforcement leather layer around the heel, and an extra leather heel counter cover inside.

And stitchdown construction. This (and the fact that it's fully lined) means these boots are quite water resistant, and can be resoled multiple times.

They have the whole production process filmed here. You can see exactly how much work goes into making a pair.

Tbh from a functional perspective, I can't think of one thing that would be better with the Docs/Solovair style. The soles are much more durable on the jim greens, they use a proper steel shank, lots of space inside for insoles double lined... Solovairs are goodyear welted which isn't necessarily better or worse than stitchdown (the most expensive boots in the world like Whites or Nicks are usually stitchdown). Maybe the goodyear welt makes you a bit more isolated from the ground (more material between the outsole and insole), but they're less water resistant (stitchdown is very resistant, like a storm-welt). And if you use thick insoles, the jim greens are probably warmer.

Here's a cool resoling video. It's for the rezorback boots, but tbh while the upper part has a different design, the resoling process is entirely the same for all of their boots - they're all stitchdown construction...