If you are entering the lease with the intention to purchase at the end, the residual value does not make a difference in the cost of the car as you are still only paying for the total agreed purchase price plus financing charges. Yes, if you would finance the entire residual over another 3 years (in addition to the 3 year lease) you would end up paying more in interest due to the extending time you are taking to pay the car off (6 years vs your stated 4-5 yrs) but not significantly more than if you took a car loan out for the same time period.
You are also forgetting that your monthly lease payment for those first 3 years would be significantly lower than your financed car loan payment would be. If your intention is to purchase, but you lease in order to get the additional $1,500-$3,000 in incentives, you could put the money you are saving in monthly payments for the first 3 years into a savings account to use to pay down the balance when financing the residual value.
Let me give you my lease as an example. The agreed cost of my 3.8 AWD Ultimate with options was $47,884 and after incentives, $44,884. The residual value at the end of the lease is $30,624. Total principle paid over 3yrs is $14,260, total finance charge is $2,219, acquisition cost $595 for total costs (not included taxes, reg, etc) of $17,074. Monthly payment is $474 for the lease.
A 5 yr auto loan with 1.9% would result in monthly payments of $837.21 and you would pay $1,956 in interest ($263 less than lease) over 3 yrs and the remaining balance would be $19,700. You would also have paid $13,076 more in monthly payments which could be used to pay down the residual upon purchase if you saved it (which would bring residual amount to be financed to $17,548.
In this case, leasing the car saves $2,142 ($3,000 incentives less $595 acq fee less $263 additional financing costs for 3 yrs).
I am not saying that leasing is always the best choice, but when looking at the current incentives from Hyundai, I think a lease is the cheapest way to get a Genesis especially if you qualify for the competitive owner $1,500 and have good credit. Essentially not leasing is like giving more money to Hyundai.