I agree with you, that's why I said the inside-out tracking would not be happen on miltech HMD anytime soon. However as far as I recall the Hololens army-version is using SLAM, but this project has already been canceled due to power and other issue. The infantry-level HMDs still seems like experimental.
Well yes, HMDs for infantry use would benefit from SLAM since the application would be totally different to HMDs inside a cockpit, on a fighter jet that utilises the ship-board sensors to relay data to the pilot.
Whereas a soldier would rely solely on the HMD for 'extended' first person situational awareness, such that the use case would indeed be analogous to commercial and consumer applications where having a standalone, inside-out tracking system would be an advantage as much as a requirement.
Such considerations wouldn't be a concern, like I said, for
flight helmet-mounted displays. In fact it would be a
disadvantage, the simple point being, just ask any pilot if they would rather have half dozen cameras on their head, or around the cockpit instead.