#she fails

In short: hell to the fucking no

It’s a shame that there’s no proper official definiton of the term, thus this’ll be a bit vague.

It’s true that Mikasa’s physical power doesn’t come exclusively from herself,  her relation to the Ackerman clan plays a big part in that, and it probably would be more believable if Isa had already explored this part of the story, but oh well.  However, Mikasa’s strength doesn’t just come from that. Like the others, she went through years of training, mastering abilities and techniques, and growing even stronger, through hard work, something that came from herself.

And even if her strength wasn’t her own, it still wouldn’t make her a Mary Sue, after all, Mikasa has found herself unable to achieve victory many times. She was unable to rescue Eren from Annie in the forest and would’ve likely been killed if it wasn’t for humanities strongest showing up. During the armored titan fight she wasn’t able to make a difference, and when the SC attempted to rescue Eren from RB in the fields, her physical strength was useless against Reiner, and she even ended up heavily injured and unable to fight even against the mindless smiling titan, spelling her doom if it wasn’t for Eren and Hannes. She was almost shot in the raid on the Reeves company, Bertholdt was able to hold his ground against her in human form in Shiganshina, and her thunderspears were useless against CT. And Hange bested her on the rooftop. Does that sound like a Mary Sue to you? 

Although Mikasa has often relied on her superior physical strength, it has proven to simply be lacking too often. And thats the thing about Attack on Titan: simply being the strongest guy around simply doesn’t cut it. As Eren put it in ch 72, they had to combine their forces in order to truly bring about change.