It’s a matter of opinion. Personally I don’t agree that Chowon or Kaeun would fit the group. Chowon is doing similar concept in her group, but it doesn’t hit. Karin also seems to mature for izone concept. It might be true that there were bribes, but at the same time it could be that they didn’t accept all bribes, just of the trainees they were okay with. There’s no way to really know
As an additional comment on this one: Chowon did a similar concept in her Cube group and has shown she can fit in with that sort of concepts, that's all that counts. Whether it was a success or not is not on her, that's on Cube and the song they chose.
As for the PD's rigging, no, I don't think they had a wide choice of bribes and candidates of bribing companies, I think it was just those few candidates of just those few companies.
But what was the PD's own choice was the actually valid candidates that needed to get booted.
Think about it: they didn't just simply go for the #11 and #12. They went for Kaeun and Chowon, specifically.
I think they chose them because they either thought they could get away with it because those two were more acceptable choices, or because in the PDs' opinion those fit the group the least.
Kaeun, the PD's could use the 'too old' argument, and in the show you'll notice that suddenly in 1 of the last episodes, a jury comment pops up in how Kaeun was maybe too old for cute concepts.
Chowon, she was the most dark skinned of the remaining candidates, and she had been an outlier for a long time before her epic rise.
We'll never know how things would've been if the PDs hadn't rigged things or what exactly happened in the background, of course. But some things jump out regardless, and 1 of them was the actually valid candidates these PDs opted to remove.
