There was a time that DECs (mainly retired 121 Captains) had a high washout rate. However in 2018 they changed the DEC program. Now you are hired and paid as a DEC but you are initially trained as a FO. You then get 3 rotations as an FO before you go into the normal upgrade process. This gives the DEC a chance to learn the aircraft and the work before having to check out as a Captain. This has greatly reduced the DEC washout rate. Now the majority of washouts are FOs in academic training or in the Mission Fit. Once they get to the sim at DFW very few washout.