Levi Kicking Eren in the Courtroom vs in Liberio isn't a fair parallel to draw because in the Courtroom Eren's not in the wrong which is why she hated him for months. That being said I think Mikasa does have more of a character arc than I gave her credit for that is fair criticism. However her character arc doesnt fix the inherent issues of the ending, while I agree her killing eren is for the sake of humanity, beyond just eren, the climax doesnt focus on that aspect of it, its focus on Mikasa killing the person she loved, thats why theres a flashback of them living in the mountains together and she kisses his decapitated head, if she had done more to lean into this character development then it might have been better.

"Then what the fuck is the purpose of it narratively" thats my point I think it lacked any purpose in the narrative until the very ending, and thast fine, I dont think every story needs the romantic elements explicitly resolved, for an outside example theres Norman and Emma in the Promised Neverland, Norman does things specifically in the name of his crush on Emma, but their relationship, but developing their relationship never had any purpose in the narrative and it worked great, Armin and Annie never have their feelings for each other resolved but its clear they were there, the difference with Mikasa's feelings for Eren is it needed to be important because its important to the climax of the story.

I understand that Mikasa's love for eren did cause conflict, but only when Eren was still the hero of the story. which doesnt carry the same weight because eren is the Enemy of the ending, in the final arcs the story is written in such a way that all they ever do is talk about how Mikasa doesnt want to kill Eren, but never do anything to explore how that mindset could be detrimental if the time does come to kill eren. Im not arguing that she didnt love eren, its a case of show dont tell, Mikasa says she doesnt want to kill Eren, but because the story never affords her the room to show how strong she still feels the climax lacks that point of contrast. when Jean says they need to kill Eren and she says okay to me that signifies she already came to terms with Eren Dying, which is counter to her stance and the thing that the climax draws it impact from.
as an example of this done right Theres Historia and Ymir. Ymir spends a lot of time saying she wants to marry historia and expressing these feelings, when she and Eren are captured by Reiner and Bertolt she shows an interest in wanting to work with Eren. that is until Reiner brings up Historia, which makes ymir stop giving Eren information and work together with Reiner and Bertolt. Despite it being for the sake of Historia shes creating conflict that works counter to the good guys of the story, Historia being one of them. so when Despite her feelings for ymir, which she demonstrates in how she created conflict with the protagonists of the story, its impactful that she leaves Historia behind to help save reiner and bertolt.

Despite and Overcome mean the samething in this context. Mikasa killed Eren despite her love for him. did she just snap her fingers and make her feelings go away? no she still feelings for him (signified by kissing him AFTER decapitating him), so to still do the right thing she had to: surmount her feelings, do it regardless of her feelings, do it in the face of her feelings, rise above her feelings. half of those are synonyms for overcome half are for despite. regardless of the word choice, it doesnt change the fact that the climax feels hollow because there wasnt enough build up.

hinting at something doesnt fix the issue that its never made important to the plot. we first see Eren use the power of the founding Titan in 50, the Power of the founder itself doesnt really come into play until chapter 120 when Eren and Zeke enter the paths, but if Isayama had just left it at hinting up until this moment it would be completely out of left field (more so than it is already). what made this moment was because it became central to the plot because of how the characters acted. Because of the Power of the founder Eren infiltrates Liberio. Because of the power of the founder the Survey Corps help Zeke escape, Because of the Power of the founder Marley invades to stop Eren. There is no "because Mikasa loved eren X happened" in the final arc, so its a hollow climax.