Well your last point but I need to say this
they dont just have not to share the same 3-D space but they have to be spatio-temporally seperate
if two universes share the same temporal axis, then they can be spatio-temporally separate but if they share the same time, then they are not
if they can be affected then they are not seperate, Two universes A and B are spatio-temporally separate if there is no point in A and B time and space that are in both
actually not anymore, different timeflow is not really prove of different space-time, even inside the same spaces we can have different timeflows, an example is our universe, there are places where there are faster or slower time flow, even hundred of years difference does that mean those parts of the universe are a different space-time? Different timeflow can be caused by a lot of things, gravity or the rate a universe is moving or expanding e.t.c.
does whiz open a portal when traveling through these universes? if yes then that means that is not a feat against them been spatio-temporally separate, but if he does it by going super fast, then it is really prove of them not-separate
you can check out
this thread it is about the new tier 2 standard