That BABIP difference was not luck. Bettances was among the worst in MLB for giving up line drives. His HR/FB% was also significantly worse than Hader’s. Lots of line drives = high BABIP.
If I were to suggest Matt Barnes was worth 2 top prospects plus from another team, you’d be among the first to shoot it down as ludicrous. Yet Barnes strikes out nearly as many as Betances, gives up fewer line drives (re: hits), fewer home runs, and unlike Betances, has a high BABIP that actually might be carried by some bad luck. Oh, and Barnes is cheaper and has more control remaining...