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.
I've been fiddling with and mentally masterbating the MR route and noticed the fastest guy (about 2 hours, his GPS track is somewhere) followed the regular MR trail within about 10 feet. I, myself am still trying to figure the quickest way (for me, no youngster) to get through the waterfall area just below Iceberg lake........
Butch, Go farther west, past the waterfall/seeps, maybe 100 yards, and there is a nice dry access.
Not sure where it is in this CalTopo/Google-Sat view, but it's one of those lower-left to upper-right paths--several of them "go". The seep is the dark area on the lower right. Zoom out to see Iceberg Lk.
Doug Sr. once described this route to me as a shorter alternative route to Russell, also avoiding some of the sand slog. I searched the internet a bit, hoping to find a gps track. I did find a few folks that had tried this route, but none that had succeeded.
Went up to Iceberg lake on Monday and messed around with 3 approaches to the lake. First approach, just past the first waterfall was mossy, muddy, possibly fastest if it would have been dry. Next about 100 feet further west kinda the same, last went way west (like posted) and it was easy peasy. No scrambling at all. Save that for the final 400......