The whole point of the 20 reppers is that it should be very difficult and taxing. Watch any real 20 rep set and you'll see how difficult it is. Its not meant to be some housewife cardio kinda thing.
If you can do Deadlifts after a 20 repper, youre not using enough weight.
If you can do 20 reps after a Deadlift session, youre not using enough weight.