I don’t know anything about the “slabs shortcut”, but the photo shows a route that looks plausible.
Many years ago, I had an interesting conversation with Doug Sr. My fastest time on Whitney (3:29) involved soloing the East Face. Doug and I agreed that, if you had the balls and the skill, the fastest way up was to solo the East Buttress. It’s much more direct than the East Face or the Mountaineers’ Route.
