I guess you could say that, but I think it's in a decent zone where it is.
not unpopular to the point of never getting fan art, popular enough to where she got a few figs back in the day, but not popular enough for every other guy to call her his waifu or for boorus to be spammed with x rated fanart.
I guess some of the downsides to not being that popular, is lackluster merch, most of which coming from the VN with the same image plastered on all the stuff, but the popular anime itself didn't get much for some odd reason, and I do wish there was more official artwork out there.
But I suppose she was still popular enough to snag a spot in the Toy's Works Collection Niitengo Key Memorial figure set that was released not long ago... even though, truth be told, they were doing 2 characters per show, and air just has 3 real candidates... and that's another thing, she's just a side character, who's incredibly overshadowed by the main heroine.
but it could be worse, some don't get half of any that.
So I'd say it's in a nice place, just enough for a few nice things, but not to much that I'd have to deal with the unpleasant side effects of popularity.