Your KDA, your CS score, or anything else related to your individual performance DOES NOT influence your LP loss/gain. The only things that matter is whether you win/lose, whether or not the enemy team had a higher team MMR than you, and if your own MMR is higher/lower than the average MMR of your tier/division. That's it.
1.) If you win you gain LP, if you lose you lose LP/
2.) If the enemy team has a higher MMR than your team, you will gain slightly more LP for a win and lose slightly less for a loss, and vice versa if the enemy team has a lower MMR than your team.
3.) If your own MMR is lower than the average MMR of your division, then you're going to lose more LP than you gain, making climbing more difficult because the system thinks you're higher than you should be. If your own MMR is higher than the average MMR of your division, then you will gain more LP than you lose, making climbing easier because the system thinks your lower than you should be.
If your MMR is around the same as the average of your division, then will lose around as much LP as you gain.