If you play a lot of hardcore and want to get back to core, the best way I go about it is to take a break from the game completely. For about 3-4 days. Then when you finally play again, you just go straight to core and it'll feel "normal", if you know what I mean.
But when you switch between the two modes, core just seems ridiculous when the halo jumping, drop shotting, etc all save them from dying.
Anyone who supports DLC of any kind deserves a swift kick to the balls... repeatedly. Take a stand! Don't let companies take advantage of us!