Something needs to be done to penalize players with 1000+ games as one champion and <2 KDA

This is a very clear sign that the player has no decision making skill, but can likely still get away with it in half of their games because they know every match up so well that they're basically playing from a script.

Decision making and mechanical skill should both be required to win games and climb, not one or the other. This isn't healthy.

EDIT: The issue is players who average <2 KDA over their entire lifetime with that champion, i.e. a Teemo main who has 700 games as Teemo and a 1.2 KDA average over those 700 games. Not players who have a poor KDA in a single game.