Yes, they have the worst miles redemptions overall (however it is great for some routes), I feel the rest of the airline and FF program are better than the others, which they may be banking on for keeping customers. They have the best on time performance. Their planes are nice, service is great, lots of flat beds in J, large network with partners (although the new earnings on partners is a major downgrade), etc. I choose DL even though I fly out of a UA hub because of all the other reasons, despite miles being so tough to redeem. Other aspects of the FF program like choice benefits, 100% earnings for gold, unlimited complimentary upgrades (compared to using 500-mile UGs on AA). Also it seems from what I read that DL upgrades are more frequent than UA.

I think that DL is banking on the fact that their other strong points will make up for the terrible use of their miles. Remember, mileage redemptions are only a small part of the overall experience.