So to me the "I love the person you are" stuff rings hollow because in a decade neither of them will be the people they are now in significant ways.
Aha—then the best thing to do would be for them to reconnect after losing touch with each other for a decade, because then they would be starting a “childhood friends” relationship, and we all know from reading manga that those bonds are just about eternal.
As usual, you guys are talking psychology while I’m talking storytelling—fiction is filled with stipulated “happily ever after” pairings that would most likely be disastrous nightmares in real life, and, judging by the divorce statistics, the odds in real life are not great for any two people staying together, no matter what the circumstances.
In this case, there’s no evidence that Yuzumori will necessarily change as a person more drastically than Mimika will as they both mature, and the whole point of the time-skip chapter is to establish that Yuzumori’s appearance has already changed, and Mimika still likes her more than ever.
If “that’s not how it (usually) works in real life” were an ironclad objection to every unlikely or implausible element in a story, I’m pretty sure there never would have been a romance genre at all.