The main difference is that you turn into an animal of some sort in Shurima, and you keep your body in Mt. Targon. But in terms of power, which ascention would give you more power?
Well it depends, one is magical transformation, the other is having a presence inside you from which you can draw powers. I'd wager that the Ascended of Shurima are more powerful because their human bodies are modified to suit the powers they were granted, where as the Aspects are effectively borrowing the powers from something within them that exists within the bounds of a mostly unmodified human body.
Overall because being an Aspect and Ascended are fundamentally different comparing them is flawed in and of itself.
They're not at all related to one another. Taric's "ascension" isn't a magical thing, it's literally just his ascent up a mountain. You go to the top of Mount Targon and then a magical thing happens to you if you're chosen but it's not "ascension" at all.
ascension of shurima is definitely more powerful, because it changes the life form of the ascendents. mt.targon's ascension simply allows the person to draw power from a powerdul being like hoe leona draw power from the sun.
Aureilion states that Targon's magic is crude but potent
he makes fun of ascension, not even giving it the benifit of being potent
by the logic of Aurelion being the most powerful being (so far that we know of, perhaps competing with bard and kidred as they are also, aparently, cosmic powers) and the best view on this, the Aspects are stronger than the Ascended.
interestingly enough though, what IS an aspect? apparently pantheon is the aspect of war, but he's also no longer himself as he lost his body to that power as it took him over, but Taric and Leona are still themselves most likely? it's complicated.
there's not really a way to answer it without a direct statement, though I'm in support of Targon.
Targon is the stronger power of the two. Shuriman Ascension is only using the power of one star (our sun), compared to the vast cosmos Targon itself has access to.
In time, it could be said Shuriman Ascension would be just as strong, but Shurima itself was undone. The Ascension ritual(s) will most likely never develop to a comparable point now.
Shuriman Ascension only tries to use the power of One Star. Mount Targon Ascension tries to use the power of countless stars, constellations, and probably even galaxies.
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