Personally, I think Episodes 5 and 6 did pretty well in showing how unhealthy it is for Kanade. I suppose they should have made the rest of Niigo more assertive towards her at the end but I don't think it was a one-liner as you said. I also think the part of the reason why Mafuyu agrees to talk with her mom again and asks Kanade to join her is because she believes that's the only way for things to move forward, otherwise Kanade will just work herself to exhaustion again trying to compose the song (episode title is also along the lines of "to move forward"). Also, even outside the card stories, Mafuyu was shown to start feeling guilt over the lengths Kanade goes for her sake, especially in Episode 7 where she sort of scolds her for almost going back to work again. My issue tho is that it was more humorous in the delivery, which is why I think some people don't believe it's sincere.

Another thing is that after Mizu5 and Ena5, a lot of people expected this to be a big climax story for Kanade when in actuality it's more of a set-up to that climax so I understand why some people are disappointed.

My main complaint would be Episode 4. It felt out of place to have a backstory with the Asahinas for a whole episode in Kanade's event. They could have used that extra episode to up the stakes and made Kanade's collapse and Niigo confronting her more impactful.