They were complimentary vehicles. Basic difference is that the DT is on a 4-ton chassis, whereas the WLF is a 6-tonner. Ok, those designations don't mean an awful lot outside the military but the point is they are different sized vehicles. The DT was a medium wrecker, the WLF a heavy wrecker.
DT has 2 booms of 5 tons capacity each which can be used linked together or separately. They are powered in luff and hook raise/lower but not in slew, WLF M1A1 has a single boom of 7 tonnes capacity which is full-powered. This means the DT may be more versatile as a wrecker while the Ward is more like a crane.
DT has a larger engine so obviously its power/weight ratio is much better being lighter as well. This is why most of them retained their petrol engines while the WLFs were commonly dieselised. Being heavier, the WLF is a better tow vehicle and it also has a 21-ton rear winch which the DT lacks. They both have front self-recovery winches.
That's all I can come up with off the top of my feeble nut. There's probably more to come if you're not bored yet...