If I understand correctly, we now know that the New Marriott/Starwood program credit cards will offer fewer miles per dollar of general card spending:
$30,000 = 60,000 New Marriott Points = 25,000 airline miles (0.83/dollar)
While Arrival Premier offers:
$30,000 = 60,000 Arrival Miles = 42,857 airline miles (1.43/dollar) -or- 35,294 JAL miles (1.18/dollar).
Is there a better way to earn Japan Airline miles?
If you spend $30k on this card you will get 50k JAL miles or 1.67/$. So probably no better way.