2 MOA or less to 600 Yds ?

That question also depends on what you’re shooting. 55g will struggle at that range to keep it tight, but 77g types will be able to keep it together longer out at distance. With my handload 77g and my WOA 18” spr barrel I am confident at 600, but a little less confident out at 700-800 yards. But I can still hit steel at that distance repeatedly.
 
Exactly, 2 MOA rifle at 100yds should print 2 MOA as far out as the bullet will remain supersonic. Whether you and the projectile’s bc can figure out the wind or your glass can see the target at xyz distance doesn’t change the rifle’s capability.

Many ARs are 2 MOA