I've killed 3 with 300BLK in the last 2 years. Barnes 110gr VOR-TX ammo. All boiler room shots.
1 was at 150 yards, stumbled 15' then dead.
1 was at 110 yards. Hit the ground on impact, got up, took one leap and crashed 20' away. Dead.
1 was at 75 yards. "Ran" (plowed is more accurate) about 45' then passed out and died.
I'd say it's effective. I have not tried subs yet for hunting, though, and probably never will.
I've taken 2 with .223 in the last year. One was a base of neck shot. (Just about anything from an AR platform other than 22lr would work for this) DRT, 175 yards. 64gr Gold Dot.
The other was a boiler room shot at 120, 55gr Hornady pointed soft point. Deer flinched when hit, stood for a second, then kinda shrugged, sneezed a cloud of blood, walked about 3 steps, wobbled, fell over and died. Heart and lungs were shredded.
One of my hunting buds has been using a .223 for years, hasn't had to track any more than 75 yards, most died within 20.
Whitetail are not hard to kill. Shot placement trumps caliber.