saying Carlsen plays as well as Karpov at his best is delusional.
How can you be sure that Karpov played better than Carlsen does? Chess has evolved since Karpov was the best player in the world 30 years ago. I don't think Karpov necessarily played better than Anand and Kramnik at their best either. He was a greater player but if he played better chess is hard to evaluate.


How can someone who has never won a World Chess Championship be rated above most World Chess Champions?
Because best players and greatest players are two different things. I think Carlsen plays stronger moves than Steinitz did, but I think Steinitz career achievements make him a greater player. If "five best players" mean the players that played the "best" chess I'd rank Carlsen ahead of Steinitz, if it's a question of the greatest players based on career achievements I'd rank Steinitz ahead of Carlsen.