To this day Morphy is an unsurpassed master of the open games. Just how great was his significance is evident from the fact that after Morphy nothing substantially new has been created in this field. Every player- from beginner to master- should in his practice return again and again to the games of the American genius
--Mikhail Botvinnik
Just because engines didn't exist don't make him a better player, they just explain why he might not be as good. But transporting someone from that time and giving him a modern rating based on his play relative to people with engines and a century of analysis isn't really fair either.