Addressing Her WeaknessI've talked to a handful of people who started off liking Sayaka's character but then end up not liking her much by the end of the series. Based on my conversations with them, it seems as though they view her as being a weak character. I've also read complaints that Sayaka is a weak character because she's physically weak compared to the others, doesn't have a strong resolve and despairs over a boy of all reasons. While people are certainly entitled to like or dislike characters, I wanted to address some of these points here because I really think Sayaka is a realistic, well-written character. Naturally, I am a little biased considering I obviously like Sayaka enough to make a site to her. Even so, I hope you will at least consider what I have to say in response to these viewpoints.
Does Sayaka's resolve falter and weaken? Yes. Does she despair in every timeline? Yes. Even if we were to assume the only reason she despairs is over losing Kyousuke (which it's not), is it really unrealistic for a middle school girl to feel losing a crush is the end of the world? Developmentally, no. Is it unrealistic to want to feel appreciated when you save someone or do something good for someone? Of course not. Sayaka struggles with a number of really intense, "ugly" feelings from the time she becomes a magical girl until she turns into a witch. Losing Kyousuke becomes a lot scarier when she's already feeling like a monster from losing her humanity and isolating herself from her friends for the same reasons. Sayaka was a dreamer, an idealist and someone who really just wanted the best for everyone around her. Jealousy, hatred and intense anger/hurt are new for her. They go against everything she felt she should be and she felt nothing but guilt for having them. Further, having negative thoughts and feelings created a vicious cycle for her. Sayaka is down for a slew of reasons, which causes her to have not so good thoughts toward Hitomi, Kyousuke and others. In turn, she realizes those thoughts and feelings violate her idealistic sense of justice and then she feels like a failure, which only makes things worse. Saying Sayaka despairs over a boy is only looking at her story from the surface. Sayaka despairs because her self-esteem, sense of self and view of the world is completely shattered. She's a failure. She doesn't deserve to be loved. She doesn't deserve to have people who care about her. She's nothing more than a living, talking corpse who pretends to be alive. These are the thoughts going through Sayaka's mind, and are at the core of why Sayaka despairs.
I think Sayaka is a very realistic character given her developmental stage and circumstances. Love and attraction, tension and competition in relationships with friends, figuring out how to process being mad at and hurt by someone you care about, etcetera, are all tasks for people her age. Thus, experiencing feelings like jealousy, regret and anger are very much part of the human experience. However, magical girls aren't given enough time to process and work through these feelings. The second they start doubting, cursing the world/themselves, or have feelings of regret, their soul gem begins to corrupt. Now throw in the fact that her soul was ripped out of her body and stir. Sayaka's perception of herself and the world take a number of blows right in a row. Had she been a normal girl, she would have likely had an emotional break down, picked up the pieces and moved forward. It would be a learning experience in relationships and emotion regulation. Her story showcased an incredibly difficult time in her life, and due to supernatural reasons, it was cut short before she could realistically have the opportunity to deal with it. The fact that Sayaka was able to reach a peaceful acceptance of everything that happened to her and come to terms with what was really important in the end before becoming a part of the Law of Cycles indicates to me that had she been given more time, she would have gotten through it. Sayaka was able to take her tough feelings and mature emotionally when she had the opportunity to take a step back. Therefore, I think Sayaka is not only realistic, but also a strong character.
"A person who falls and gets back up is much stronger than a person who never fell."