Jallen - two points.
First, the interest rate is negotiable. Different lease companies have different rates. And you can play one lease company against another. You are presuming the lease is through the dealer and the dealer's leasing company. You don't have to lease the vehicle through the dealer.
Second, the residual value is negotiable. By your own admission different mileages are available. That goes strictly to the residual value of the vehicle. But even there, different lease companies can use different residual values.
I urge anyone considering a lease to go online and determine their best lease options and shop them against the dealer's terms and conditions.
I had a leased vehicle, and the lease was not through the dealer. I shopped lease companies for rates and residual values; and shopped dealers for the best vehicle price.