The problem with the Blackout (for me) is that although you can shoot subsonic and supersonic interchangeably, the best setup for subsonic i.e. SBR/suppressed isn't the best setup for supersonic. So it's not really a one upper platform.
This is going to be true of most anything: To get a multi-purpose setup, you are going to be less than optimal for one or all of those purposes.
I've been playing with the .300 Whisper for several years. It used to be common for people to use adjustable gas blocks, multiple gas blocks with shutoff valves, etc. if they wanted to shoot both subsonic and supersonic ammo through the same gun.
What impressed me about AAC's iteration of this cartridge was the development on the gun side of the equation, where they found a gas port size that would cycle both subsonic and supersonic ammo with no changes to the gun, gas block, etc. But again, there is no free lunch. In order to do this, they are limited to a narrow range of bullet weights for each velocity, and only a few powders with the appropriate burn rates.
AA1680 seems to be by far the best powder for subsonic bullets in an AAC-designed barrel. The problem is that AA1680 is
loud compared to many other powders. (I have found H110 and AA#9 to both sound quieter to the ear than AA1680).
By going to a larger gas port, you can use quieter powders. But then you end up with a gun that is overgassed for supersonic ammo.
So you can take your pick, build a gun specific to the one type of ammo. Or get a more flexible gun that comes with the built-in compromises. I'm not saying one setup is bad, or one is better than the other. It just boils down to what the individual wants and what their priorities are.
