As much as I love the lore it exaggerates about the champions power in a false way
Take 
for example, described to be the first being when reality itself was formed and him being able to destroy and form stars at his grasp, and in-game he feels really underwhelming because most champions beat him (like a yordle scout using poison darts) which makes the whole powerful celestial part a bit questionable.
Not to mention he is massive based off of lore, I watched this video comparison a while back where Aurelion is so massive that his eye is the size of Graves full body. He is by far the biggest being in Runeterra.
I know that it would be somewhat impossible for Riot to make his real size work in game but I feel that such emphasis about his size and him as a celestial dragon makes him in-game a bit disappointing not to be rude.
Other champion examples of a similar case would be...
2 literal essenses of death, 2 hunters who supposedly lived for aeons based on their in-game voice lines. Can be killed really easily by anyone dispite them being the Ethernal Hunters, making their theme not exactly accurate. While Kindred's R that stops all life from dying inside the circle is the one of the only abilities in the kit that somewhat fits the theme most.
"How long will we be together? Forever more."
.
Described to be a literal mountain, still as small as any basic character in game.
.
Described to be the cause of why people in (name of region) had been having nightmares every day. Yet thematically in game his ultimate is the only ability that scares players about him because the rest of his kit is underwhelming.
