It has advantages over 5.56, there is no doubt. But do they justify the cost, that’s the big question?good summary if interested; https://fenixammo.com/pages/the-ballistics-of-5-56x45mm-vs-300-aac-blackout
cliff notes; a 5.56 under 10" is pretty handicap, and that's where 300 shines
If seeking a compact package and reduced length from adding a can, it's a pretty awesome round. A 5.5" barrel 300, can still launch a 110gr almost 1800 fps. Night and day to most pistol rounds. Cost effective?.....not much beats a 5.56 for cost.
Also the 110gr Vmax Barnes really turned me on to 300 blk. It's nasty. Not scientific but drops pigs notably more than my 5.56 in 11.5" with 55gr/75gr. Not that 5.56 doesn't get the job done, but most I hunt with have all switched to 5"-9" 300's shooting a 110gr vmax.
It's hits hard and just more pleasant to shoot out of a short barrel suppressed, less gassy.
Subsonics are fun to play with too, but I seldom shoot them and can't comment on effectiveness.
If you want a hard hitting round in an AR15 platform, there are better choices, designed as such. The 6.8 and the 6.5G seem to be the go to rounds. These are far superior to both 5.56 and .300.
If you’re after compact and subsonic, .300 becomes a pistol caliber. There are more compact PCCs available.
I guess the coolest thing about .300, and what has always intrigued me, is that by merely changing ammo, you can go from pistol caliber to short range rifle.