One more data point. We are on Explorer Tokyo - Tokyo - Vancouver next April. My early investigation of frequent flyer tickets led me to add air back onto this itinerary ($2700 plus $249 secondary hub per person). I was investigating what options were likely and found a Singapore Airlines flight from LAX to NRT. When I looked at what it would cost to book the flight it was 123,000 KrisFlyer miles per person. I then transferred 246,000 Chase Ultimate Reward points (earned from $82,000 of travel spending) and used DL miles for AUS-LAX and YVR-AUS.
So, I now asked TA to remove Regent flights. I still haven't ever used Regent air but our cruise next June is a no-brainer to use Regent air so will finally get to experience the planning process.
YMMV
Marc