Here's the back-end of Langley taken from the outlet of Sky Blue:


The Major General is to the far right in the second photo. The "standard" route coming down west from Langley is to drop down to upper Soldier and contour around the Major by ascending this boulder wash:

Yes, ascending, because you can't really make it around at the level of upper Soldier due to huge boulders & trees. So you end up descending a bit down the drainage (still very bouldery) to catch this gap between upper & lower Soldier lakes.
(This gap is the standard x-country route for entering Miter basin for those coming from either NAP or Cottonwood pass via PCT & lower Soldier. You can also follow the trail down to Rock creek from lower Soldier, then follow up into Miter, but it's too much loss IMO. I've done the gap twice and the trail once.)
It's maybe a couple of hundred feet loss/gain, so no real big deal. But, as you mentioned, you sort of end up coming down to the same level to walk through Miter basin regardless of the route you take. Since you get to the same general spot, the no-risk way is to simply do what everyone else does. If you decide to come down north of the Major, I'm not sure you save much (if any) time, but you might end up with some surprises that could waste time/energy.
As for Crabtree pass, the plateau is around 100+ yards from the top next to the 3 tarns. You can also camp in the 10-15' wide sand wash right before the pass. It's sandwiched between two shelves on either side that provide a nice protected spot. You can't see the detail on the topo map, but it's clear on the sat photo:
Crabtree pass camping spots