I think being able to boil a character down to a single sentence isn't a good or bad thing. Some of the most compelling characters in fiction could easily be described in a single sentence.
Here are some examples that come to mind for me, ignoring great side characters and focusing just on main protagonists who have stuck with me, and trying to go into multiple genres.
Spoiler tagged cause somewhat spoilery. And some of these go a little more interpretive. My point here is well written characters absolutely can be summarized in one sentence because that is all that it is, a summary. And you always lose details in a summary.
Going into literature:
Quasimoto- An adopted deformed man with family issues and a crush on a gypsy.
Don Quixote- A chivalric, insane man who creates his own problems and fails to grasp reality.
Ishmael- A whaler sharing a bed with a cannibal while witnessing a descent into madness and revenge.
Edmond Dantes- A betrayed man who has gotten rich and plots to enact his vengeance on all those who have wronged him.
Paul Atreides- A kid from a spanish-style planet who ends up on a desert planet and becomes a messiah leading a revolution and empire before falling.
Roland- A gunslinger who will reach the tower no matter how much or who he must sacrifice to do so.
From Film We Got:
Ashitaka: A cursed man trying to create a balance between the strenuous sides of man and nature while searching for a cure.
Oscar Schindler: A greedy nazi who ultimately realizes the atrocities of Nazi Germany and does his best to save and spare the Schindlerjuden.
Charles Foster Kane- A man who kept grasping for more when the things he truly wanted were always in his grasp, and only lost because of his greed.
Jim Hawkins- A boy with father issues who grew up on stories of pirates finds a map to a treasure and goes on a journey while connecting with the villain.
Ellen Ripley- A smart and strong woman who gets caught up in the consequences of corporate greed in the form of an alien or aliens.
The Iron Giant- A giant robot that is possibly a weapon of mass destruction finds companionship and a strong moral compass leading to it growing into a hero.
From Television:
Kiritsugu Emiya- A man who dreams of becoming a hero and saving the world but adheres to a philosophy and methodology of sacrifice and "ends justifying the means."
Aang- A kid out of time who has to learn how to be the bringer of balance in an era of war while also coming to grips with how the world has changed.
Alvin Murphy- A selfish person with immunity to an apocalyptic virus who goes through phases of messiac cure bring, psychotic ruler, and eventually better human than most humans while still being a little more zombie.
Eleanor Shellstrop: A terrible human who supposedly woke up in heaven and over time has problems with ethics that eventually prove that humans can change and that society and structures around humans can change.
Legoshi- An anthropomorphic wolf coming to grips with his carnivore nature while also developing a relationship with a rabbit and deer while also dealing with the problem of a murderer.
Ashley Williams- A man who has survived B-Movie horrors having to face those horrors again at an older age with the help of some allies.
And From Video Games:
Lee Everet- A possible murderer having to take care of a little girl in a zombie apocalypse while dealing with troubles from outside and inside the group.
The Undead- A cursed individual rising up and taking on challenges to preserve or end an equally cursed world with unknown motives or unknown reasons to persevere where others go hollow.
Squall Leonhart- An emotionally stunted child soldier finally opening up to other people as he realizes his capabilities in an inherently unfair world, while recognizing how he contributes to the cycle.
John Marston- An outlaw given a chance for freedom who does the work of a corrupt government to give his family a chance at a good and honest life.
Laura Croft: A rich enigmatic tomb raider who gets caught up in mysterious situations and conspiracies, often times connecting to her past and her past traumas.
Artyom: A survivor of a nuclear apocalypse who travels the world of the russian underground surviving and dealing with the growing threat of mutants and violent tribes of humans.
