My Sierra thinking about backpacking is that once past the point of "one day in", everybody up there has their own load to haul...(I am sure not adding any more, especially weight of yours.)
Agreed that just leaving thousands of dollars worth of gear, unprotected along one of our Sierra's busiest trails seems foolish, but somehow, up there, it never feels crazy/ never worried about it much.
At Whitney specifically, (a unique situation), within the close knit backpacking community, (with everyone having cell phones), the chances of someone just getting a Whitney permit, then making it up to Trail Crest and finally stealing a pack, and returning/ getting past the portal again un-seen...doubtful.
I pity the guy who tries.
I would worry far more about your car left at the trailhead, where the people who do not backpack hang out.
Mountainman who swims with trout