The fact that one girl worked hard and had a "better character arc" does not warrant them being the winning girl. Life takes many twists and turns, and you never know where you might end up in the end. You may put all your guts towards reaching your dream but ultimately there's no guarantee you'll achieve it. Having that one person in your life also does not guarantee your happiness because 1) you're not entitled to mutual feelings and 2) happiness and fulfillment will not be brought to you by someone else's or something else's existence in your life, it comes from within you, understanding that you're the only one who can make you happy.
Fuutarou spent a long time contemplating his feelings. He knew, just like we did, that he has to choose one of the girls if he wants their and his feelings to amount to something. He knew that a choice had to be made. But your heart is what it is, you can't force it to feel a certain way. But it also knows exactly what it wants. He just had to ask it and search for his feelings. And by the end, his discovery was that throughout all of this, he deep down loved just the one.
You might have the urge to say this just happened to be that way, it could've all easily ended up another way. And you'd be right, in a sense. The reason he chose her IS the circumstances that lead to that point. All the experiences that he had up to that point had built up to this moment and culminated with his heart's final verdict, and who are we to rule against his heart? I know this is all fictional and I'm starting to sound kinda deranged but this is very much how it happens in real life. People just happen to fall in love as they live their life. The saying is as old as time itself: we do not choose who we love.
This series was in the back of my mind for a long time after I finished watching the second season. I knew that we'll end up with one of the sisters as the bride, but I just couldn't imagine how anyone could objectively choose that one girl to end up as the winning girl in the end of the story. And that's exactly it: there is no place for objectivity to be had in the final decision. I knew that it would absolutely feel cheap if the outcome of the story had some rationalized reasoning behind its existence. Cuz that's not how love works. Feelings are beyond the reach of your rationalizations. Love does not obey any logical reasoning, and neither does it have to. You love who you love, and that's just that. And I'm glad that this series made me realize that once again.
