One that comes to mind for me: “Whatever doesn’t kill you makes you stronger” is not always true. Maybe even only half the time! Are there any phrases you tend to hear and shake your head at?
You bring an interesting point! So there’s a Japanese phrase this reminds me of: Shouganai (しょうがない) which translates to “It can’t be helped”. For me, this hits differently than “It is what it is”. Perhaps it’s the context, as I know it’s said about natural disasters like tsunamis and therefore has a connotation of the “getting on with fixing it” like you said.