Paulsen played a surprisingly modern looking Sicilian in Morphy’s day. What Morphy wouldn’t understand is all the Hedgehog and Indian systems.
Remember, Morphy was at his best in open positions, but he played before Lasker, Nimzo and Capa codified positional rules of the game. He played without the signposts we all use today. That’s incredible! But his play still shows weaknesses in positions that today we take for granted.
One idea that he had only a dim understanding of was how to play in isolated Queen pawn positions.
When we consider just how much knowledge has accumulated since Morphy, it’s amazing he played at the level he did!
honestly, i cant even see morphy beating 13 y/o magnus, considering how he fared agaisnt karpov and kasparov lol