If I think about it, I realize that I can name many recordings where Mark made mistakes on stage in those days, and also many mistakes by John, but NOT ONE SINGLE mistake by David!!
His rhythm seemed always tight in time to me, never a wrong chord, or such.
I am not saying that Mark and John made too many mistakes, just the 'normal error rate' that simply happens on a gig, and maybe David was just lucky that his mistakes were not recorded on one of the bootlegs.
I rather want to say that David seemed very concentrated and reliable as a rhythm guitarist. I always liked his rhythm guitar very much!