devtrackers.gg
You can only transfer the DLC if you link both of your Steam DbD Account and your Epic Games Account to the Behaviour account - you will still need to own the game on both platforms in order to do this.
Grades are not used for matchmaking, grades that you can see show how much time someone has played in a month, not their skill level.
Matchmaking is done on an MMR/SBMM system which is hidden.
Your MMR doesn't decrease if you take a break from the game for a little while, which is probably why you are noticing a disparity at the moment.
