I didn't say that. I'd say that if UA enters service on NRT-BKK, NH will likely reduce or eliminate service on NRT-BKK, presumably keeping HND-BKK.

Why would I say that? Because they're joint venture partners. Although the JV does not extend (AFAIK) to intra-Asian fares, the whole point of the JV is that they are managing TPAC capacity together. Any passenger that UA convinces to fly SFO-NRT-BKK on UA instead of SFO-NRT-NH on NH, or on mixed metal, does exactly nothing for them. The only reason UA would open this route would be if NH is capacity constrained and can't add additional flight(s) on its own.

I don't deny that those flights are full. It doesn't mean that they're profitable. The correlation between load factors and profitability is a lot weaker than many people imagine -- because the question is always, "how much did you have to discount the seats in order to fill the plane?" (It doesn't mean they're not profitable either, mind you).