Phil Rudd and Cliff Williams lay down some tight groovy rhythm, but I am sorry. I can't accept that it is difficult to play. Cliff often sits on just one note. Sure they have great time keeping but so should any bass player or drummer worth their salt.
It's not technically difficult to play and it's easy for people to think "yeah, I could do that no problem"
But can they really? Maybe they can copy existing drum and bass patterns but how would they fare working up new material with the band? Would the feel still be there? A couple of drummers played with AC/DC when Phil Rudd took time out and the band sounded a little more wooden, just didn't have that swagger. Could any old bass player convincingly replace Dusty Hill in ZZ Top?