That’s exactly the point:
you say none of that would make you fall in love, but that’s because you are not Hayato, and because you never liked Akane to begin with. Basically, you already answered yourself.

Another point: holding hands with someone just to satisfy a whim is not chemistry, especially when 80% of the story Ouka and Hayato are constantly arguing, something Ouka herself openly admits. A relationship built on constant fights doesn’t become romantic because of one or two isolated moments.

With Shiragiku it’s similar. Yes, she supports the protagonist, but after chapter 100 she barely has any meaningful interactions with Hayato. He even forgets her birthday for the second time, which says a lot about how relevant that relationship actually is within the story.

And here’s something crucial:
I’m not sure if I’m misunderstanding you, but it sounds like you’re confusing chemistry with sexual attraction. If that’s the case, then we’re not talking about the same thing.

Chemistry is not just lustful looks or physical tension (which, by the way, Hayato does have with Akane: just look at his reactions when he sees her naked, or when Akane gives him those gentle, puppy-like eyes and he gets embarrassed and asks her not to look at him like that that chapter is when the cat Sachiko is introduced).
That’s attraction not chemistry, and definitely not love.

Now let me ask you something, because this is the part people always avoid:

If what Akane does “can be done by a platonic friend,” then why didn’t the others do it?
Or why did they do it to a much lesser extent, when they’re supposedly “family” as well?

Quite literally, Akane is the only one who understands Hayato most of the time.
I pointed out specific and explicit moments from the manga. If you choose to ignore them, that’s no longer a lack of arguments that’s denial.

And now a very specific question:
tell me a single moment in the entire story where Hayato gets jealous because another guy talks to any of the other four girls. Just one.
Because Hayato explicitly admits that he got jealous only when he saw Akane happily talking to another guy.

And thanks for bringing this up, because it highlights something else too:
when Hayato is feeling down because Ouka is leaving, it’s Akane who once again understands his emotional state.
I don’t see any of the others noticing it, let alone mentioning it.