If you want a Rioter response, good luck mate. Rioter's VERY RARELY ever post on the PB boards.
As far as your particular punishment goes, what others say has absolutely no bearing on your punishment. You are responsible for your actions and your actions alone, that's it. You breaking the rules is grounds for punishment, period. It doesn't matter if others started it or were worse than you since your punishment isn't about them. Also, just because your report card only shows one game doesn't necessarily mean that it was the only game that contributed to your punishment. The system will only show you 1-5 recent games that you were punished for, but other games it doesn't show you could very well have contributed.
As for the other players, unfortunately we can't know for sure whether they received a punishment or not. The feedback system doesn't always tell you if someone you reported got punished, and there's know way to know if someone is chat restricted, so it's possible that may be the situation here. Also, when it comes to instant 14 day bans with no prior chat restrictions, if I'm not mistaken there's really only a few phrases that seem to trigger that (such as racist slurs or specifically saying "kys"), so it's possible that the other player avoided them and, again, only got a chat restriction.