I think it makes sense because if they damage themselves it hurts their chances of surviving against the coming attack despite how strong we've seen our heroes to be. Divide and conquer style.
I like that Hange calls that out just like you said.
Yup, even though she talked about how much she idolized Sasha ever since she saved her they didn't really show her so I wasn't thinking about what her reaction would be to hearing all that.