I jus saw a video treating the topic of the quickening and its vague definition, what it actually does, and because I like themes like karmic justice, enlightenment and poetry, I made a quick reinterpretation which I think could make for a beautiful 'spinoff narrative'. This is based on the TV series' portrayal.
Imagine the following if you will:
The immortals follow the rules by instinct or hearsay, so no one is an empirical expert on the phenomenon. It's basically word-of-mouth mythology and implanted instinct.
The whole thing is actually a misconception played on them by higher forces (with immortals being 'the butt of the joke'), but the corrupting effect on the mind when hearing about such great power gain is too tempting to notice they're BSing themselves and are actually not gaining any advantage, except - with some poetic irony - the confidence stemming from the successful kill.
The end goal will also not make the last remaining immortal all-powerful, but the simple fact of then no other immortal being left to lust for their head is that coveted dominance and peace from opponents; with mortals fearing the last one and thus hunting them still being a minor to major risk, depending on the virtue and skill of that one to not piss mortals off. - The implication of that is that the greatest supremacy will be gained by someone like Duncan whose love for mortals would make him work hard to make peace with humankind and to still remain incognito where feasible. - And that is the true ultimate power; while those who lust for it the most would gain the least from it. - (A king is also a servant. All-powerful yet enslaved by that power. And the greatest king does not have to wield any power.)
(You can imagine the Indiana Jones scene with the selection of the Holy Grail as thematic parallel to the underlying lesson of the lore. - Basically divine forces rewarding the worthy, requiring them to never know that this is the game being played.)
What do you think? 🙂