I never once said he would get tired. i said he was up against someone who is amazing at draining energy. He is far better than anyone on the Avengeds. Nefaria's stamina has nothing to do with this. His entire body is a sponge for ionic energy, and he is completely dependent on it. Surfer is one of the best energy absorbers in Marvel. That is a very specific advantage for Surfer, besides him also probably being stronger/more durable/faster as well.