Absorbing Man, despite the name, doesn't really absorb or drain powers. He kinda mimics the properties of what he touches. For example, when he touched mjolnier, he didnt absorb its powers but duplicated its properties both physical and magical which is why he can contend with Thor most of the time.
Not sure if touching Superman would grant him Superman's powers, most probably yes which is why IMO, Superman would be hard pressed to win against AM and the Wrecking Crew. The Crew are all packing magical weapons and are all significantly strong enough to do some damage albeit, not strong enough to take him out. But they'd put some good hurting on Superman and AM would be able to finish the job.