I feel the side characters would have a bigger appearance in the story. And there were a sudden change of pace throught the story too. So I disagree, it is plausible to think It was axed, even whithout the author's comments about it. The real question is: why the annoyance by people saying it was axed?
I'm not annoyed by people saying it was axed, I'm annoyed by people assuming something without any evidence.
For example, why do you feel the side characters would have a bigger appearance in the story? They don't have any hanging plot threads or unaddressed developments. They are exactly as involved as the story would lead you to believe they are, and there's not really much they could do that would change the outcome in any way.
It seems to me like you just wanted more, and you're projecting that on to the author regardless of what she has said or indicated.
There is a sudden change of pace because the story hit a crisis when Kashiwai is confronted with the fact that she's not happy being one of three lovers Like I said, when a car is driving towards a wall, things are going to change fast once it hits. That doesn't mean the wall is a surprise. You can see it coming. It's a wall.
I'm not even saying I know with certainty that it wasn't cancelled early, but I think it's worth it to point out that there's not really any evidence to suggest that this isn't exactly the story Akiyama-sensei wanted to tell.