Hi cyberdevil3,
I don't think you're experiencing input lag, but rather you're exceeding the game's maximum turn speed. Read this to get an understanding of maximum turn speed, which when exceeded leads to a performance issue many people incorrectly attribute to input lag: Understanding Mouse Settings. Destiny has a very low maximum turn speed, which is why it feels like input lag to you. If you were to play Call of Duty: Black Ops III or Infinite Warfare with the same mouse settings you would not feel the same limitation.

Without going too far into the geeky minutiae of mouse performance, here's how to set up your Death Adder Elite with KeyMander. Your mouse uses the PMW3389-T3QU sensor (seems to be a version of the PMW3366 sensor) which unlike non PMW-3366 mice, does not have a native resolution so you can set it at any resolution (in 100dpi steps using the Razer software) without the impact to performance that mice with interpolated resolutions have. This basically means you can set the mouse to our current sensitivity limit of 10000dpi without issue. I've read this mouse does have some smoothing (pixel averaging), but most people say it is not noticeable unless moving very slow speed at higher dpi settings (like when sniping at long range targets). I have not personally used this mouse, so I would set it at 10K and test it out while learning to stay within Destiny's turn speed limitation. I've also seen recommendations for low dpi PC gamers using the DA Elite to set it to 1800dpi which has no smoothing, but requires more in-game sensitivity which for KeyMander users means using higher mouse sensitivity. The bottom line is to try it out and see what works best for you, but no matter what you must work on getting a feel for the game's maximum turn speed.

Let us know if this helps.