Is there anyone who could make an argument that there is another tennis player that could beat/could have beaten Serena Williams when Williams had her serve and her ground game on full display?
Hard to say because fitness was so different back then and the equipment was as well. I think it's safe to say there is no one in the history of women's tennis who is as strong or powerful as Serena. I think a baseliner like Chrissy would have been creamed no matter how strong Chrissy got. But maybe someone like Steffi who mixed up her shots and had that great slice backhand, or Navratilova who had an all court game and loved to come to net, maybe.
But when Serena is as fit and focused as she is now, I think realistically no way. In the past, though, it seems that often the ones who gave her the most trouble were the clay court specialists who had lobs, top spins, slices, drop shots, changed directions all over the place, and kept Serena out of rhythm.