Creator of Things
While on a very practical level I agree with this notion, I can't quite see it as being accurate in the face of actual published text.IME, the player facing setting whether playing with only the 3LBB or with all of the 3I setting has always been the same: a collection of semi-random independent worlds that present whatever situations the Referee desires.
To take one example:
The 1981 edition of the rules introduce the notion of Travel Zones (Amber and Red). These are worlds noted by the Travellers Aid Society as being dangerous.
In the setting specific materials of the Third Imperium, hover, Red Zone became an entire world or system interdicted by the Imperium.
Let's be clear about what this means: there is an adventure on a world, and the interstellar government is already there in some form to prevent you from getting to it.
That is a very large presence and effect of the Third Imperium. It is well beyond the scope of a collection of independent worlds.