The pre-sear is especially important with long cooks, because it kills surface bacteria. The first time you get too much lactobacillus hitching a ride on your short ribs will be the last time you skip out on the pre-sear. (Lacto isn't dangerous; after all, the protein is pasteurized in the bath, but the final product will smell awful).
I'm not sure what you mean by "drying out the edges, making them leathery". I think I can just say "no" on that.