If you've seen Joaquin Phoenix in first teaser trailer to Joker you wouldn't judge Ellie's appearance based on her back in this position. Almost anyone will look the same way sitting like that. And don't forget the fact that she lives in post apocalyptic world where she has to be strong to stay alive
To me, Joel doesn't look unathletic at all, he's strong, durable, and far more fitter than the other people in the game, as far as I can see
And Ellie, although is not better than Joel, is imo Well characterized, I preferred its phases in the first game, to the ones with Joel, much more sense of survival and danger
She was a little non mature, but she still was 14 y. O., so in tlou2 will be very different, we know this for sure
Also, for the ones complaining Ellie looks too muscular, remember she lived in a safe zone for 5 years or more, with supposingly enough food, medicines, place to have proper rest, and many, many scavenging expedition and weapon, fight and physical training
If she had been on the road for five years, could have understood all the complaints, she would have looked much more emaciated, but imo this way is not too strange
Not at all even close to impossible. General martial arts practice for teens I have seen countless women in better shape than that and instructed a large number of them. Actually very unremarkable overall compared to some.