Alright so to iterate my logic/understanding here:
- According to older guidebooks, Subspace is not connected to the Living World or Afterlife (via the original definition of 'macrocosm')
- There is no indication that it's connected to the Kaioshin Realm
- Sugoroku Space and the Time Chambers exist in Subspace
- We know it can be reached by being dropped mid-teleport from the Living World to Kaioshin Realm
- From Freeza we can tell that the Time Chamber is not considered as part of the 'universe' (whether that means the Living World or Universe 7 itself we can't say)
And the possible structure for universes that I'm seeing here is roughly:
Universe Bubble (Universe (Subspace, Kaioshin Realm, Living World + Afterlife))
So the two interpretations are:
- The Subspace is not part of Universe 7 because it has no connection to the Afterlife or Living World and no known connection to the Kaioshin Realm. Goku arrived in Sugoroku Space from Kibito Kai dropping him mid-teleport from the Living World to Kaioshin Realm and Freeza being in a Time Chamber exempted him from the 'strongest in the universe' wish.
- Universe 7 is actually much larger than we can quantify because it contains the Subspace in addition to the Living World + Afterlife and Kaioshin Realm.