Large-scale desertion didn't start on the Eastern Front until very late in the war. That was because the Germans had started to replace their effective troops with children, crocks and old men who had received minimal training and were led by inexperienced officers and NCOs.
However, for the most part, experienced conscripts fought just as well as anyone else. Not running is about morale, training, discipline and comradeship rather than how one got into the army in the first place.