Lol sounds like making excuses for bad storytelling
Not really. See, we all walk into this with the awareness that most harem manga end with him selecting one in the end. With the exception of say the 100 girlfriends manga, this is precisely what you will get without fail. You read enough you see this.
The fact that they do this consistently means it's a trope. Which doesn't mean it's a bad thing. It's just a pattern you notice over time. And with that pattern too comes an element of predictability. For instance, Claire is definitely the center girl of this story. Meaning she helps and supports him and he doesn't have to be in conflict with her. This plus amount of time and emotional closeness means she's inevitably the most important to him. Should the manga settle on her, that would be that.
When you are able to see the ending, then you have to stop and ask yourself: if the ending is predictable, then what's the point in reading it? And the answer is just this: a story is that: a story. You don't read a story to know how it ends. You read the story for the adventure itself.
Hence why I said the journey is the reward. Sunk cost fallacy, by the way, means trying to post hoc justify emotional investment. Since we are nowhere near post hoc at this point, it makes no sense to claim that enjoying the journey is just a sunk cost fallacy.
Oh, right, at no point do I try to justify this manga as having good storytelling. The story is bland, the characters are basically summed up with a word, and the story is the same story we've seen dozens of times.
Thing is, I read this fully aware of this. But, like watching black and white samurai films, this too is a guilty pleasure. Plus I rather like seeing if any of the other girls in this are kind of like me. I like a good protagonist character I can see myself in. If you think the story is bad, you're more than free to drop this. Nobody will notice or care.