Those new 6.8mm rounds are crazy. For context, your typical rifle chamber pressure is ~60,000 psi (5.56mm, .338 lapua mag, etc) and these 6.8mm rounds go to ~80,000 psi. Punches above it's weight. Very interested in this space lately.
yes it was clearly designed for short range engagements - not exactly same application as 7.62x39 as a general purpose medium range infantry cartridge. the military/contractor folks I know wouldn't even think of using blackout at ranges where anything above 250 yards would be anticipated.
the blackout is also unique in that the subsonic version of it was designed from the start to be NATO-rifle-platform compatibile with a suppressor. and due to even lower velocity, even shorter range (definitely 75 yard and less).
also fairly unsure on its performance vs. modern plate based body armor vs greater velocity of regular 556 nato, 6.8 as you mention, etc.