I think the Beatles as a pop group will never be surpassed. They were good enough musicians to pull off the tasks they set themselves. That is not saying they were brilliant instrumentalists. In fact they achieved considerably more than many bands, who had much more basic musical ability. That in itself was extraordinary. Looking back, it is hard to remember what pop music was before they arrived. For me, they were the first ever adult pop group. I do not believe anyone else could have brought that off.
I'll go along with the comments of Bee-dubya-ell on this one. Somehow "Sergeant Pepper" had a very special aura in 1967. I think it is almost impossible to explain why objectively forty years later. Maybe this is a subject, which does not lend itself to objectivity?