taking action against these kinds of things is always dangerous because however you try to solve it, there ALWAYS will be teams that get disadvantage, and will complaint.
a simple example to show it: a team can have sacrificed his cup game to get a league win against that team, and then afterwards the team gets banned, or the user quits playing.
HOW is anyone ever going to compensate that???
I think the best way to deal with these situations is to just try to play your own best game, and have fun playing, and if something like this happens, ok, bad luck, or good luck, however it turns out at that time, and keep believing that if you are doing a good job, you will raise in the ranks, no matter what happens. Just have patience and don't let such things ruin the fun you have.
I know it's not much, and probably not what people hope to read when they are anxious for a solution, but I am positive it is the best way.
In real life things like this happen as well. When you are in a competition, teams drop out too, teams forfeit games too, and teams even hand over wins to others, just to get in a better position, or to help out friends, or get people they don't like down.
It tels a lot about the team causing it all, but it also tell a lot about remaining teams, how they react to it all. Keeping up good spirit and take it as sportsmanslike as possible for your own and your own team will only make you more respected, and the achievements you can make will give you more satisfaction.
If these things do influence the endresults so much, then the comoetition is tough, and that's good, but it also means your team isn't good enough yet to diversify from the rest, and instead of spending time blaming the system, it's best to spend that time to try to improve even more.
They are not your friends; they dispise you. I am the only one you can count on. Trust me.