You're in gold league with a bunch of level 1 accounts. They end up playing eachother meaning the one that one party for sure looses in GOLD league to A level 1 account means bad news for their ELO score with this modification. The winning account would gain some elo but they beat a level 1 so the modification doesn't reward them as much. Because beating a level 1 account in gold (where you can have level 8 commons) means it's not much skilled involved.

So the modification keeps an eye on the league you're in... also keeps an eye on how leveled up cards are.

Which actually would be awesome for actual players beating teams with under powered teams. That's some great skills and should be rewarded.