Do you think the story would be as powerful if the old man had successfully brought the marlin to shore?

I think there is heroism in Santiago's failure to bring the great fish back intact. Hemingway draws a distinction between two different types of success: outer, material success and inner, spiritual success. While Santiago clearly lacks the former, the import of this lack is eclipsed by his possession of the latter. One way to describe Santiago's story is as a triumph of indefatigable spirit over exhaustible material resources. As noted above, the characteristics of such a spirit are those of heroism and manhood. That Santiago can end the novella undefeated after steadily losing his hard-earned, most valuable possession is a testament to the privileging of inner success over outer success.