Both traction control and diff lock have benefits. a spinning wheel on one end can stop a 4x4 with an open center diff and traction control stops the spinning wheel and then lets it go so some drive is lost at the other end of the vehicle, if one end of the vehicle has good traction this can drive you over the obstacle without any wheel spin.
Having said that I used to lay out off road courses for main dealer off road weekends and on one such section I was using a Disco 2 and a Defender 90, we went down a grass covered hill (about 30 deg) then turn right on the hill through a gate and turn right back up the hill. The turn right up the hill could be done by every one who tried in the D2 even first timers but nobody could do it in the 90 it even took me about 12 attempts, this was all down to the open center diff and traction control.
so the best is have both.