Their is a difference between viewing someone as a tool and seeing them as expendable while some of the actions you describe are merely pragmatic: Primarchs are intended as both generals and statesmen putting them in charge of the legions and assigning quarters in the palace makes sense as does giving them latitude to handle things as they see fit. While the downside of a killswitch is that their is always the risk of it being exploited by an enemy. Not making more is almost certainly a limitation of technology and resources along with a dash of paranoia (The space marine codex heavily implies he was the one who destroyed every record of an essential component of creating Primarchs). The lack of failsafes was frankly another example of the Emperors arrogance.
A valuable tool is still a tool.
That said we do seem to be drifting off topic here. If you want we can move the conversation to PM.
