That is incorrect. I have a pair of Hathorn Smoke Jumpers (10''. black smooth leather just like the ones pictured) and the arch support is the same as with my White's Farmer/Ranchers (which are Smokejumpers but with a 700 sole instead of the lug sole). I don't feel a difference with regard to arch support.
The black smooth leather on my Hathorns is at least the same thickness as the brown smooth on my White's. I don't have a White's in black smooth for a direct comparison but the quality of the leather looks excellent, with tight, even grain and no visible defects. It's extremely tough, takes a while to break in and is unmistakably a workboot leather. I read somewhere that the leather for White's, Hathorn Hi-Line and Hathorn boots is cut from the same hides, and that White's gets the nicest pieces. It would make sense but I have no idea if it is true. Also, even the best parts will still look like black oil tan, i.e. decidedly un-glamorous. Anyway, the leather looks and feels great.
Hathorn hardware (hooks and eyelets) looks identical to White's. The soles are the same as well (Vibram 100F with red center lug), but "only" stitched on – no screws on the Hathorn sole. If you don't spend your workday walking on hot, smoking ashes, you probably won't need the screws anyway. The main difference is in the craftsmanship. It's hard to describe, but when I look at the boots side by side, the Hathorns look less refined, less detailed than the White's. The stitching is not as precise and a bit wonky in several places (purely cosmetical), the backstay has a simpler shape and the whole boot looks more plain and workboot-like.
However, the most important difference for me is the fit. Hathorn SJ are made on a different last than White's SJ. And for me the White's last works a lot better. Where I get a precise fit bordering on too narrow with the White's, the same size (12.5D) in Hathorn is actually too wide. The White's SJ last also looks better, its shape is better defined and has more character.