Yes, some steels are stiffer than others under the hammer. Back when I did hand forging demo's I would always try to have 1084 mainly because it moves so much easier than other steels. I have always found 5160 to be pretty stiff and W-2 feels even stiffer. Surprisingly L-6 is one of the easier steels to move by hand. Its not just your imagination. Just heat the steel up more and that helps a great deal.