You're assuming that you spend prevention costs perfectly when you can't.
The money that you spend on someone to prevent/reduce a problem is completely wasted if that is not suseptable or is struck by something else. (Also, the cost to deal with obesity and diabetes together is less than the sum of dealing with obesity and diabetes separately.) It's also wasted if the person gets the problem anyway.
And, you're still ignoring the benefits of early death.
The money that you spend on someone to prevent/reduce a problem is completely wasted if that is not suseptable or is struck by something else. (Also, the cost to deal with obesity and diabetes together is less than the sum of dealing with obesity and diabetes separately.) It's also wasted if the person gets the problem anyway.
And, you're still ignoring the benefits of early death.