It's actually not a subtle nerf at all. By stressing a single ship (and thus the entire list) you shut down AM for at least 1 ship for a full turn.
For example: stress bot hits one of my 3 AM ships. All 3 get stress. Going into the next turn, AM is basically shut down.
Ship 1 does a green, takes focus. Whoops, AM is useless because the other ships haven't cleared their stress.
Ship 2 does a green, takes focus, whoops, ship 1 already has a focus, so it doesn't get anything.
Ship 3 does a green, takes focus (because it still doesn't have one) and AM does jack.
obviously there's another option:
Ship 1 does a green, does some non-focus action.
Ship 2 does a green, does some non-focus action.
Ship 3 does a green, focuses and passes.
But you have just basically defeated the point of AM by forcing every single ship to do a green AND forcing the final ship to take the Focus action, all for what would have been a single point of stress had it not been for AM.
It's absolutely an excessive nerf, all to deal with a focus token through AM. And that's just assuming a single stress. Most stressbots are built to pass more than 1 stress, or if you set it up right, double stress one ship and single stress the other ships.