Not doubting your shopping, but I happen to be looking at a Hong Kong Itinerary, too. You made me look up NCL, Oceania and Viking. I'm not seeing what you're seeing.
Agree the NCL Sun is smaller, and the Balcony fares are right around $5,500 for 11 days. Club Balcony cabins are higher, so I'm comparing base balconies on the other lines to Balcony cabins on NCL.
Looked at Oceania for their cheapest Hong Kong itinerary also 11 days, sailing in their cheapest balcony and they were running $14,000.
Viking's cheapest veranda is running about $10,500 similar itinerary but only 10 days.
So, once again, I'm leaning towards NCL.