My thought is Ellie's looks change one because shes older, but two because shes permanently changed by this dreary, immoral apocalyptic world. TLOU1 shes young enough to think she can still be saved, be redeemed, innocence preserved
TLOU2 her appearance is stretched out, thinner. Shes world weary now. And the idea behind the violence being too much is because for the characters of that world...its too much. Likely purposely more gruesome.
You don't see gore like this in Uncharted 4, not because they couldn't achieve it. TLOU is supposed to be brutal and endless. Its not always the most pleasant game to play, its not a breeze
And though the gameplay is smooth and varied, its almost disturbing people w speed runs on youtube and highlight reels of kills. Think thats just a case of not the audience ND wanted to reach