Damn, I couldn't even have imagined this kind of plot development. It was funnier because Aqua dismissed the whole idea of someone imitating Ai, yet was so shocked by the result. It's no wonder Akane has been called an excellent theater actor a couple of times now. She has the skills and dedication to really become someone else for a play, even if her own personality is just too nonexistent for a show. The way she analysed and researched Ai got some psycho vibes.
It's not necessarily a huge problem if she's quite different suddenly. After all, everybody knows she attempted suicide and was absent for an episode (or a few). The audience would rather have expected her to not come back at all or to come back with a visible difference, I'd say. Although I suppose a difference this huge might not have been expected.
I can't help but feel Kana was talking through the fourth wall a little bit by saying Akane not dropping out might not be good for Kana herself. If Akane captures Aqua's attention like nobody ever has, because of her Ai impersonation, Akane's existence next to Aqua ought to fade.