One issue you might run into is Riot being unable to differentiate between someone leaving on their own accord and someone being disconnected due to technical issues. If someone disconnects due to power failure, internet disruption, or any number of computer issues that require a restart, I don't feel like banning them is going to make the community any better. Certain circumstances are not trolling and Riot has nothing in place to quickly suss out which are which in any reasonable time frame.
Just as an example of something that I feel you might put me on a ban list for after your amazing game: This week, I ran into the unfortunate problem of an entire hub in Texas going down for Time Warner cable, making me lose my connection to the Riot Client, but still be able to do other things on the internet. I was at the 17 minute mark of a game and suddenly was Attempting to Reconnect (for at least 4 minutes). I exited out and tried to get back in, but never made it past "Logging in..." before it gave me the error message. I tried this for about 30 minutes before I found a thread about how Time Warner was having issues. This information didn't help my team when I couldn't reconnect. You'd probably have Riot do a quick ban on me just because I left the game. But it wasn't something in my control and Riot has no way of knowing why it was that I left.
For now, the system we have in place is all we have, where teammates just have to report leavers at the end of the game and hope there is enough of a pattern that Riot hits the players that have left multiple games with multiple reports. As far as I know, at least those leavers can't enter another game until the one they were a part of originally is over. That's at least 20 or so minutes they are effectively banned from ruining someone else's League of Legends experience. Sorry to hear about it happening to you in ranked though.
Good luck in your climb.