The ARC cartridge lineup’s “thing” is that they use Grendel-based cases. They use high-BC projectiles at modest velocity, mimicking larger cartridges (edit: exterior ballistics) in a 5.56 mag length. Their other “thing” is that even though Grendel has more case capacity than 5.56, it operates at lower pressure due to the bolt. For 6mm ARC, Hornady publishes bolt gun data that uses more pressure in order to get the velocity you’d otherwise expect from the case capacity. Kinda like the handloads for Grendel or SPC you read about on the internet that are “totally safe*” but exceed anything from the Basspro shelf.
.338 ARC’s idea is to have subs and supers that operate at a smaller difference in pressure and gas volume between subs and supers, in comparison to .300 BLK. In other words, full time suppressed with no messing with gas blocks or buffers between subs and supers; just change mags. While I know people do that with BLK, there’s a pretty big gas drive difference between subs and supers there, and it is probably at its finest using supers unsuppressed and subs suppressed. Why Ruger is taking this path with a bolt gun, though, I have no idea.
I’ll probably set up a semi- .338 ARC SBR someday like an optimized PSD gun or LVAW to play with that idea.