I switched from DL/Skymiles as my primary program because of no one way redemptions, flipping to AA. True, AA eliminated stopovers, but one ways give me a lot of options to mix and match, since I have miles in a few programs plus Amex and Chase transfer options. BA's Avios short haul redemptions within Europe are pretty great. Occasionally I have to buy a short haul connector flight, but it isn't the end of the world.
The bigger issue with DL for me, even after they move to one way redemptions, is DL's redemption rates. For 2015, a one way US-Europe saver award in biz is 50K on AA, 57.5K on UA and 62.5K on DL. US to North Asia is 140K roundtrip on DL in BusinessElite, 5K MORE than the 135K that AA charges for FIRST class bookings on Cathay. BE is a fine, but not top level, product and definitely not on par with first on Cathay.
DL has been such a disappointment over the last year, with every move seemingly giving the middle finger to customers, from pulling availability access from Expertflyer to raising the MQD requirements. And now pulling stopovers. It all adds up to a 'the only thing we really care about is our bottom line" message.