There are a lot of assumptions here.
(1) You have met the first three requirements. I doubt that many people have.
(2) The 6% is continuously upward with no volatility.
(3) Income will not disappear. One comment already touched on that. The investment would be a hedge against that possibility.
(4) You meet the 6% goal. It is a projection.
The math works fine if all of the assumptions are met. An alternative of doing both would cover (3) and (4). It all depends on your comfort level. Not having any debt gives you a lot of options.