You're missing the part where we have no guarantee that either explanation is correct. Blizzard is free to go ahead and reveal that the Dream is actually something else entirely.
I'm not denying your claim of it being limited to Azeroth. I'm denying your claim that we have definite information about it's origins and nature, which you have not actually provided any proof for.Again do you have any proof to support the claim that the Dream exists across the Universe and not just in azeroth.
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Absence of evidence is not evidence of absence. That something isn't mentioned in the Chronicle does not mean it doesn't exist.
The Titans simply might never have bothered to check before Azeroth, not having any need for such a thing beforehand.