I think that that's a somewhat tenacious reading of Durkon's statement. RAW Valhalla is a CG / CN border plane, so it matches both alignments and someone who goes there has gone to an Outer Plane matching their alignment, fitting Durkon's statement. At worst it's him giving a quick one-sentence summary to someone with no Knowledge (Religion).
Miko was told she could visit her horse.
Beyond that, like I said above, I think that reading Durkon's statement as "there is exactly one and only one plane for each alignment, and these planes are in a one-to-one relationship with the alignments and everyone goes to the one and only one plane that matches their alignment, and no other alignments" is reading far too much into it.
Turning it around, though: We go by the assumption of RAW unless we have some indication otherwise, right? Is Durkon's statement the only indicator we have that is leading people to speculate that OOTS Valhalla might be non-RAW? Because I feel it's not really strong enough to support that.