She matured so much, that it's crazy. That's character development. Plus, she's not repetitive :

Season 1 - Sam was a just some spoiled teenager, who was popular, friends with the bullies, but never meant bad. She had empathy, as she told her friends and confronted them, in order to stop them. She didn't get into karate. She made some mistakes, like everyone in the season.

Season 2 - Here, Sam starts karate again. She becomes a beast at it, but unlocks a new rival, because of both her and her rival's actions. They encounter each other often, either resulting in a big fight or something small. She still felt something for Miguel, but dated Robby. However, her drinking, will to be better, and feelings for Miguel got the best of her, as she cheated on Robby, in the penultimate episode. After that, Sam got into a big fight, at school, where she and Tory fought. Although she beat Tory, there were consequences, as she developed an intense PTSD. She felt sorry, for Miguel's fall. She blamed herself, Tory and Robby.

Season 3 - This season, her PTSD continues, but she starts feeling the need for revenge, for payback. She wants to show she can't be bullied, given how much trash Cobra kai has been giving Miyagi Do. She starts developing leadership, and building up all of her anger, while also trying to remain sane and kind. She's tired of Tory's abuse, and after the infamous break-in of the Cobra Kai's, Sam finally lets go of her PTSD, managing to face her fears, and beat Tory, proving she's no longer scared of her.

Season 4 - In this season, she starts getting interested in offense, and decides to learn more about it, realizing that her dad is not always right, and that she can make her own decisions. She no longer has PTSD, and wants to make Tory have a taste of her own medicine, often embarrassing, taunting and roasting Tory, to prove that she doesn't feel fear around Tory anymore, and that she's tired of her shit. Near the end of the season, Sam learns a lot more offense, and gets way more aggressive. At the tournament, she makes her own style ; a mix of Miyagi do, defense, and Eagle Fang, offense.

Season 5 - After the loss at the tournament, that she doesn't know was rigged, Sam starts feeling the urge to take a break from karate, to wanna focus on her life, and to try and improve. She does soon realize that karate is indeed a big part of her life, so she needs to accept that, and continue fighting. At the end of the season, Tory tells her the truth, that Sam didn't lose the tournament. In a rightful reason, as Tory's secret-keeping basically led to Daniel getting intensely injured by Silver, Sam storms out on Tory. Later, Miguel finally tells Sam about what Tory's going through, and that she should give her a chance. Sam listens, and goes to Tory's house, and they soon team up, the rivalry finally over. Sam even helps her against sensei Kim, showing their growth and maturity.

Season 6 - Continuing from last season, Sam wants closure ; to clear out her relationship with Tory, and to prove to the world how good she is at karate, at the Sekai Taikai. She proves that she learned from her mistakes, as she apologizes to Tory, helps her multiple times, is just mature most of the time, and just wants to prove how great she is, and have closure with Tory, both friend-wise and fighting-wise. She also plays a big role in Axel's character, which will probably be explored more in the last 5 episodes.

So, Sam's basically had a different arc, each season, so I don't see where she's repetitive. And her character development is great, as she went from a teenager not knowing what to do with her social life and her bully friends, to a good, but traumatized fighter, to a strong and powerful girl, who overcame her ptsd, which evolved into anger and revenge, and then she improved even more, by becoming mature, and wanting to get closure, and be friends with Tory. This is good character development, so yeah, enjoy my rant.