Ah now this is interesting

Talos did not become a god through sheer power, like for example Mannimarco when he used the Numidium.
Talos is a conglomerate entity of Tiber Septim, Hjalti Early-Beard, Zurin Arctus and probably a few others.
The story of their life, the events and choices they were involved in, so closely mirrored the story of creation that in effect they are one and the same, apart from size.
The ascension comes from this affirmation of creation, this strenghtening of the Wheel.
This road to heaven is called the Walking Way, when you walk the walk of a god until they must walk like you.
Talos is the enantiomer of Lorkhan, a term from chemistry which means mirror image.
This is also why the Thalmor want to remove him from the mythic awareness.
Like the Dwemer their ultimate goal is to escape what they see as the prison of creation, to return to the divinity and endless possibility of the dawn.
Only their methods are very different. Where the Dwemer attempted to turn their entire race into a god, the Thalmor are trying to uncreate the world.
Talos is a pillar, a spoke of the Wheel. His existence affirmates Creation, he is a big giant 'Yes'.
His removal would destabilise the world enough for the Thalmor to attempt to uncoil the dragon and end it.