I appreciate yoru point of view, especially given the conditions you dive in, however I would contest the remark about streamlining. I mean once you're dragging some doubles and some deco cylinders, a second inflater is not going to give you any additional measurable drag?
For me also a drysuit is not practicable for more than 3 months of the year. Air temps on the surface make it unbearable (even wetsuits are put on after a dunk in cold water first. Water temps - even deep +40m /130' will be 36C/98F for 2 months of the year. Hence double bladders can have their place.
Given that X-deep decided that the Stealth Tec 2 which is a highly regarded and popular rig would benefit from being a redundant bladder system - there must be a demand and a rational for this kind of system.
As always of course there are many ways to skin a cat dependent upon other variables.