Big part is how assessable the power is, because depending on how powerful one can become, the rarity of the ability makes one seem more powerful it it has fewer with that power rather than everyone having it. A great example is Mistborn, where Mistborn are fairly rare and therefore carry more weight and power behind, and SA, where the radients are technically powerful than Mistborn but because of ho common the ability is, it carries fair less weight.
Another example is superspeed. The flash is seen as incredibly overpowered because of how fast he can move, but if it wasn't uncommon for people to have his power, superspeed would lose a lot of weight and be easily counterable
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