Shadowbans just don't work. If you're hit with one for a good reason, then you'll always have a way to check for it. Sometimes by just logging off, other times from a friend or by fetching data through a machine in a diferent location, but you'll always know it. And if you're mistakenly banned, then you will keep trying your hardest for whatever amount of time, only to randomly find out that you might've as well played offline because nobody sees you, and you have no idea why or for how long. It has happened already in multiple games, always with those results.
Honesty ELO on the other hand is a brilliant idea and I wonder why nobody did it yet.