Board Thread:Warhammer 40k General Discussion/@comment-4851119-20140323173912/@comment-8257990-20140413021010

Power Armour can't really be upgraded, true... As the Adeptus Mechanicus/Tech Marines wouldn't allow it unless the upgrades were sanctioned. However it does not require much need to be upgraded, especially if the Spartans were to fight them using standard weapons, it would take higher-tier UNSC weaponry to punch a hole through thick layers Ceramite, Plasteel and Adamantite.

However, I will agree that Spartans can be produced more easily.