For me personally, this is no problem because I only use manual recalculation 
But I agree that in the case of automatic recalculation, this may happen - and the previous route will be lost. Maybe it’s better than nothing?
Or maybe another solution… But you probably won’t agree to add the “Undo last recalculation” option to the application menu 
Such a solution would solve a possible problem of manual loading of the backup file and enable several levels of Undo. Just like e.g. in MS Word 