I can't say I've seen too much hate on here, but that's cause we're mellow. That's why I like it here best.

Still, I think you might just be underestimating the vocal abilities of say, Chisato, when you say that the others would have butchered the song.
What I've noticed with singles is that they tend to use the B-side to balance or offset the A-side. For all I know, the B-side for this has Airi not singing at all or something. That wouldn't be much consolation for the other girls though.
I was listening to Cutie Queen the other day and I started wondering how the different the group dynamics and line distributions would have been if Megumi had stayed on. Would it have been more like what we have in Berryz where there's three and a half front girls? (Yurina counts as a half of a front girl)
In general, we've gotten used to roughly 2 and 2/3 front girls in C-ute (1/3 each for Nakky and Mai), so it's not surprising that this is causing such an uproar. It's kind of like they graduated almost 2 whole members without any forewarning.
For all I know, Tsunku wrote this one specifically for Airi. Problem is, that kind of song is usually on an album, not a single. But since when has Tsunku NOT been batshit-insane? I love the guy for it, but if this is going to become a pattern with C-ute, I just feel sad for the other members.