So basically it's not worth SBR'ing
I'd say out of the 3 calibers in the comparison it's the one most
Using a short barrel involves obvious trade-offs in terms of ballistics. The numbers show that the 300 BLK gives up very little ballistics-wise, certainly much less than the other two calibers.
In fact, given that 16 inches is the point of diminishing returns, I think you're missing much of the utility (and fun) of the 300 BLK if you don't SBR it.
I think it's awesome that you can use a barrel length that is considered absurdly short in 5.56 and be just fine in terms of velocity (and terminal ballistics now that there are properly designed bullets), operation of an AR, and silencer wear and tear.
With an 8" or 9" AR upper in 300 BLK, you can now have a silenced weapon that's as short as an unsilenced M4, yet it can hit just as hard, or harder.
That very small loss of velocity for such a large reduction in barrel length is a much better trade than you get with the 5.56 or the 6.8, especially considering that the velocity in the short 300 BLK is well within the design parameters of the 300 BLK's bullets.