There is a big problem with the 300 blackout. and its ammo related...
When you use a 243, 270, 308, 3006 , even the old and lowly 30-30 or anything else like these, you have a margin of error. There is always some clown who shows up with completely inappropriate ammunition, usually out of ignorance. In most cases however, there is still enough power that a .30-06 with a bad bullet will likely still take that deer.
The Blackout can take deer cleanly. But the problem is there are a lot of totally inappropriate bullet and ammo choices available. I am willing to bet that various game managers are banning the .300 AAC because of shitty performance because clowns are using the wrong damned bullet. It may be "cool" to hunt with your subsonic suppressed 8" SBR, but those subsonic loads are almost always a REALLY bad choice for hunting big game. While some people will take deer with a .45 ACP, few people will do so with old school 230 FMJ bullets. When you load a 300 AAC with 220 or 240 grain subsonics (or worse yet, anything using a 150,180 or 208 subsonic), you are essentially trying to use a round roughly equal to 45 ACP hardball on deer..... at 100 and 150 yards. Its stupid....
The Blackout can take can deer cleanly. It REQUIRES the use of a supersonic bullet designed specifically to expand on game at AAC speeds. Virtually all .308" diameter big game bullets are designed for impact speeds that the AAC simply cannot get to, even at powder burn distances. However, there are a few bullets that will do okay in the AAC.... Barnes 'designed for the AAC" 110, Hornady 125 SST, and Noslers 125 Ballistic tip. These bullets won't cut it in a 300 Win Mag since they are FAR too fragile. But they will open well, without over expanding, when launched from a 300 AAC at speeds of 2000-2100 fps.
The 7.62x39 soviet round is a decent enough deer killer. its no moose rifle, but it will drop deer readily enough. 110 to 130 grain loads in the 300 AAC are roughly equal to the 7.62 commie round in terms or energy and performance. whatever a ruger Mini 30 or a SKS will do with a Winchester or Federal 123 grain soft point, a .300 AAC will match when loaded with a similar, appropriate bullet. There simply isn't a real margin of error of any real size when using the 300 AAC on deer. Very very few people would use a 123 FMJ out of a 7.62x39 on deer, but these same people inset on trying to use a heavier, non expanding bullet out of the blackout. Its a bad idea. Any bad rap the blackout is getting is due entirely, in my opinion, to stupid ammo choices.