> then the changes are no longer truly independent.
But the author of the code is telling you that they are independent. The author may be proved wrong if some future change accidentally triggers dependence but we as humans can have knowledge that the compiler can not have. The compiler sees a possibility of conflict and wants to protect you from yourself. That is a usability issue.
Rust is exploring techniques to allow "the author of the code" to provide finer "separation" semantics without resorting to unsafe - this is what GhostCell, QCell, LCell etc. are all about though their "usability" is still low. There's plenty of ongoing research in this space, so feel free to stay tuned for more!
But the author of the code is telling you that they are independent. The author may be proved wrong if some future change accidentally triggers dependence but we as humans can have knowledge that the compiler can not have. The compiler sees a possibility of conflict and wants to protect you from yourself. That is a usability issue.