Yeah Riot doesn't support that at all. It's just that they can't have a human system to look for trolls all the time, which is why there is Riot support, the ticket system, and the report system. No computer system can be accurate enough to detect all trolling, There was a more human system years ago, the Tribunal, where players would go to review reports and such...and issue their vote on whether a person deserved to be punished. Even with free help from players, not enough people were using the system, and the Tribunal was always extremely backed up. People would get banned many months after their toxic games.
As for harder punishment, if they are caught enough times they are getting a perma ban, what can Riot do to punish people harder than that?
As for why you should "have" to dodge and wait 5 minutes, you shouldn't "have" to, but you definitely should want to. Unfortunately, pretty much everyone on the ladder is subject to those kinds of players, across all rankings. You dodge to protect your MMR, so that you can keep climbing. It's pretty much the same thing as muting people in game. You lose chat with your teammates, potentially you mute their pings, you're giving up on information in the hopes that their toxicity won't ruin your game...just like you'd dodge for the same reason.