I don't think it's relevant either way, but I think shortstops are closer to first basemen offensively than you think.
Average OPS for SS .711 (98 OPS+)
Average OPS for 1B .744 (107 OPS+)
So, there seems like there would be a lot of overlap and for that group which overlaps or comes close to overlapping, shortstops are a lot more valuable because of the position they play.
Of course a 1b who hits .950 gets paid more than a SS who hits .711, but his WAR would be better too, so I don't understand your point.