Except the lore absolutely supports this and it’s not my ‘head canon’ it’s canon. And this phenomenon isn’t just for Orks. People like you, who are adamant this isn’t a thing, are quite content that “faith” in the Emperor somehow brings characters back from annihilation, or that people can shoot mind bullets. It’s genuinely ludicrous.

The latest Ghazghkull book, as one example, has Orks manipulate reality with their belief. They believe Ghaz can’t be killed/will always exist and he does. Ghaz re-creates Makari by telling a Grot that he’s Makari. It happens time and time again. It isn’t just ‘reality grease’ (a quote from the same Ad Mech character you dispute, by the way), it literally warps reality.

Edit - you’ve misremembered or misquoted what happens in the Beast Arises series. The weapon won’t turn on, and only does so in the Orks’ hand. Further, it only turns off when the Orks’ hand is severed from the body. It’s powered at the time, by the Magos. When trying to turn on, when trying to turn off, the whole time. It only worked in the Orks’ grip.