My FT friend just redeemed a 100K low level LAX to CPH via AMS award in business class. Before he succeeded in this, he was of the same opinion that DL miles were useless. Now he transferred all remaining balance of his AMEX Membership Reward to DL before closing the AMEX PLAT card...

Yes, DL is not easy to redeem because it requires tons of homework and the domestic portion often does not have low level... but once you are willing to spend time and effort to learn the rope on how to do it (DL forum has excellent STICKY), you would find it actually is quite useful!