@Lord Zee - Basically demi-gods are like any other divine creation in that they get as much as what's put into them. If you pour a years worth of power into a demi-god then they will have that much power for a year. The more powerful the demi-god's capabilities are the power they require, effectively determining the rate at which a demi-god depletes the power given to them. Thus, a demi-god with a years worth of power could be as powerful as it's parent god for a year or half as powerful for two years and so-forth. Like any other being who lacks a Divine Cord they cannot replenish their power themselves and they are not immortal. Should a demi-god cease to receive power from their patron deity they will slowly lose their power and eventually die of old age if they aren't slain before then.
As for deities if I were to try and quantify their power then I'd say that if the barest minimum amount of power expenditure was 1 power then I'd say a deity generates 1 power per second to a maximum of ten years worth of power. To grant some perspective on that, for example, Oao could use her power over darkness to create massive hands formed from the night sky to tear the main continent in half and that would exhaust all ten years worth of power from her. She'd require ten years worth of rest in order to return to full power capacity. In contrast Ragnageddon could use 1 power to generate a small candle flame.
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On a separate note I'll be updating the front OOC page to include some more detail regarding the recent lore that's been uncovered. I'll have a new post updating the situation at the plant spire up sometime this evening approximately.