The handholding in rust doesn't come from mut or not. It is from the borrow checker. That is a completely orthogonal language choice to mut by default vs const by default.
I will admit I hate lifetimes and am annoyed that I can't have shared references without making them reference counted. That is where I struggle and time is wasted.
The biggest problem with rust is that while I am trying to make sure I code in a rust approved way, you are off getting things done. Maybe if I had more than a hour to code a week I'd get proficient enough to no longer be slogging through all the time.
The benefit of rust is that once you get it to compile you will absolutely be rewarded with better binaries. Can c give you binaries on par with or better than rust? In theory yes. In practice no. Even the best programmers make the kind of mistakes that rust prevents. Languages like go cannot create binaries on par even in theory. There will always need to be runtime checks for garbage collection.
The question I would pose to you boss is what problem is she trying to solve in switching to rust. If you need better binaries then go for it. If you need faster development then why are you even thinking about it instead of coding?