Aromanticism and the asexual spectrum is a complex topic because it's, well, a spectrum.
Either I don't agree with folding asexuality and aromanticism together period, or I don't agree Aromanticism can be a 'spectrum' per say, since a spectrum only has a single axis. Since, on the one hand, if you're saying that aromanticism is strictly speaking a single thing, then it can't possibly be asexuality since asexuals can be very romantic and sexuals can be very nonromantic. On the other hand, if you're saying that romance is several things in terms of aromanticism, (including sexuality) then aromanticism can't be like homosexuality, which can at least be partially modeled by a 1 dimensional Kinsey scale, but instead it must be a collection of different axes, with perhaps no necessity of them having anything essential to do with one another. In this case, its not just complex because it's a spectrum, it's also complex because it's a collection of spectrums which are essentially distinct.
You're right in pointing out that attraction has several parts, such as sexual, romantic, and aesthetic, but generally asexual or aromantic people simply are not capable of feeling such forms of attraction.
This is the part I don't get. Like, say that there's a person who is asexual/aromantic in every way that they could be. Do they not find things cute? Do they not find things beautiful? Do they not feel emotional comfort? I would guess they do, but they don't feel them "romantically"? But idk what differentiates those feelings when felt romantically with those feelings when felt non-romantically. They feel the same to me. That's why the only thing that seemed like it could make the concept of aromanticism non-conflationary would be that the differentiating factor is 'attraction' itself (which I identified with emotional desperation, longing is probably a better word). Without that, I don't understand how aromanticism could be a single thing, rather than multiple related things conflated together through the term, or a tendency to not feel those certain emotions (cute, beauty, etc) in a culturally romantic context, which I don't believe is the claim, but I guess it could be.
Like, in regard to the story, what's the added thing that Yoriko needs before her feelings for Matoi are romantic? She already finds Matoi cute, is physically affectionate towards her, is lonely by her absence, sympathizes with her, admires her, finds her soul beautiful (through Matoi's music), and enjoys being with her. Why does this not count as romantic already? What is missing?