"Aromanticism/asexuality are spectrums!"
They sure are! And Alastor is on the bold-stripe, nonpartnering, romance/sex- and touch- repulsed/averse end of those spectrums! And he's actually one of the first and only examples of that end of those spectrums that we've ever gotten!
Seriously, list ANY other characters you know of who are as explicitly on this end of the spectrum as Alastor is, because I can't name a one. Everyone likes to say that the repulsed and the nonpartnering and the green/black/bold stripes get all the representation, but he is actually the only one I can name who is so explicitly like that. Everyone else is vague, and seems to be likely rose-indifferent.
Elsa seems personally uninterested in rose stuff, but not repulsed by it, and I could see her in a rose relationship eventually
Merida seems personally uninterested in rose stuff, but not repulsed by it.
Peridot seems personally uninterested in rose stuff, but not repulsed by it, maybe slightly averse at most.
Lilith Clawthorne seems personally uninterested in rose stuff, but not repulsed by it, and I could see her in a rose relationship eventually.
Ahsoka Tano seems favorable towards rose stuff, even though I and many others headcanon her as aroace, and I could see her in a rose relationship eventually.
Ryland Grace seems personally uninterested in rose stuff, but not repulsed by it.
Katniss Everdeen seems to be aroacespec, but she ends up in a rose relationship.
These are the most common aroace-coded/headcanoned characters I know of, and all of them occupy other areas of the spectrums.