I see the mechanistic POW rules as purely an artefact of the RuneQuest game system, and whilst some are happy to extrapolate Gloranthans reality from the RuneQuest rules, I am not. If a thing that can be extrapolated as a consequence from RQ can't be done in QuestWorlds, and can't be done in 13AIG, then maybe, maybe, it can't be (or isn't usually) done in Glorantha. Maybe it can. If it's awesome and improves your game, then great, have abusive or coercive POW farms!
But I would always start with Glorantha. Is it happening in the world? If so, what mechanics do we use?
Other opinions are available.