2nd Update: (possibly resolved issue!)
While I'm updating games to my wonderful brand new PS4 Pro, I'm certainly not saying goodbye to my XBox 1, or giving up on this issue with the frame rate drop.
I found something very interesting last night. Now normally my Xbox will prompt me to update the dashboard whenever I boot it up. Apparently there was an update not too long ago (Nov. 10th) and today is the 14th. My console didn't prompt me to download it (very strange). I looked up what this patch does, and it basically boosts performance in the before super slow dashboard and should fix issues like the one discussed in this topic.
So I updated the console via settings, and it was there around 678mb. Pretty large for an update (normally they're around 200-300mb), assumed it would help the frame rate issue with MKX.
Booted up MKXL, connected online, and it worked flawlessly. It even loaded the game pretty quickly in comparison to before. Since there are a lot of DLC items, it seems like the game checks all the content before it goes to the copyright screen.
I also checked to see if the game performs well offline. Well it stuttered at one point during the intros, and not since. Played for a couple hours completely offline single player vs cpu matches and no lag.
So go ahead an update your system if you haven't already. Could have been an issue on Microsofts end. In the beginning, MKX had problems due to the game checking each piece of DLC, 1 by 1 before allowing you to play normally. This was with the old dashboard. Sometimes purchased DLC characters and skins wouldn't show up, but was resolved in a dashboard update, ironically.
Let me know guys if it worked for you as well.