The streak leaderboard is pretty lame, it encourages boosting. The fact that your points don't go down if you quit, encourages quitting. There's no Win/Loss records, which encourages cheating.
Also there's a glitch I found that no one has mentioned. I was playing a match in UMK3 ranked, and I lagged out. I signed back in, and went to play MK1. I played one ranked match of MK1, then went back to UMK3. After winning about 20 matches in UMK3 ranked, I checked the leaderboards. My MK1 ranking had gone way up and I was in the top 6 for it, and I only had played one ranked match of MK1. My Kombat rating was high and I had a 20 streak in it. My UMK3 rank, however, didn't change. I wasn't getting any Kombat points and my streak didn't change.
So, you can basically rank up in any game by playing any other game somehow. I assume if you're playing say MK1, you lag out (disconnect from internet) then sign back in and play say MK2, it will count as playing MK1? I'm not sure, but something like that happened with me.