I don't believe Yotsuba is a bad fit for MC. However, if the author intended to make the Yotsuba ending, I think it would have been possible to have some more buildup. You know, some affection shown. The premise was that Yotsuba was holding back because of her guilt towards the other sisters, but show something after that guilt has been lifted, yo.
I totally agree on the build-up aspect. Totally. And there are moments when the build-up that existed were truly heart-breaking, in particular, the scene when Yotsuba was on the swing by herself.
I do strongly encourage a second read. The ending does feel like "let's push this beyond it's value" with the five views of the last school event. But if you forgive the authors, then that part isn't so bad either.
I wanted to make an annoying distinction between "Character" and "Personality." Skip this part if you're already aware, but it took me some time to distinguish them.
Personality is that part of a person we "see" when we're with them: are they vibrant? seclusive? life of the party? cheerful? gloomy?
Character is the deeper part of a person that isn't so much easily on display: patience, thinking of others, and pulling them into activities (much like Tsubame-senpai in Love Is War is the kind of sweet, helpful gal--on the look out for any loners); giving, punctual... these are traits I look for in "a good story." So, when I see an MC end up with a person who is poor in terms of character, I think "Meh; lame."
The stories I find most enjoyable are where there's a moral to the story: "Get over your darn shyness and tell this gorgeous gal you love her", not just a satisfying end: "He got the girl!" For this reason my enjoyment of The Quintessential Quintuplets was not disappointing.
Oh, by the way: here's a breadcrumb you may have missed! Scene: MC is in bed with a cold at the end of the festival where the Dance is happening outside and all five sisters are holding Futarou's hand as he is in a deep deep sleep— Each of the sisters is holding one of Futarou's fingers (five girls, five fingers, amirite?) Yotsuba, yeah, pour on the cringe, is holding Futarou's
ring finger. See what I mean by spotting breadcrumbs throughout the story on re-read?
Best Feature: Watching Futarou emerge from his sense of worth because of his amazing grades as Yotsuba emerges from her sense of worthlessness because of her lack of grades.
I simply grew to enjoy Yotsuba. Until they began to give away her past, I found her to be an enigma. When they revealed she was the girl in the photo, my heart ached for her, and I waited in hope that her love for Futarou would bear its patient fruit. The other sisters, I felt, grew to be nothing more than noise. And when Futarou confessed his love after having flopped onto the grass, I couldn't hold back the tears. And when he proposed at the playground, I couldn't hold back the excitement.
Final note: In the Anime, the campfire dance's "spell" was that whoever one held the hand of would be with the other for life, but the Manga says "Married to." Add to this: whoever kisses under teh hot springs bell will
marry the one they kiss. So, Futarou is, in a way, "stuck" with all five sisters. He can't shake the four regardless. They'll all four be with him and Yotsuba till they die. But the one he marries is, as per the legendary bell's warning, married -- which were both fulfilled. Goofy? Ohhhhhh fer sure! Sweet, entertaining, romantic? Ohhh yush!