its a lot more punishing to afk or flame in league. you can exhibit toxic behavior in 2 or 3 games and get a 7 day then a 2 week then a permban for each offense.
League player here.
Its really not lol.. dota is way more severe. Especially when you know the inner workings of the report system for league.
The thing with league is you can get away completely unpunished scott free if you have "a bad game"... its not hard to trick the bot with "a bad game" by just not showing that behavior more than once in a few games. Its riot's way of avoiding having to unban mistake cases or a bit questionable ones, they have to be consistently toxic/afk to trigger anything... and even the AFK part is handled separately with a bot and yields very little punishment.
Its why griefing is so tolerated in league by riot because their systems allow it.. and smurf accounts with some champs and BE (in a more one trickable game) cost less than a netflix movie, and don't get banned unless you're basically trying to ban it or it gets caught for being bot leveled.