Can confirm, I've NEVER got an alert from the system saying that someone i reported got punished when in the case of me reporting someone for harassing people with in-game trolling, ping abuse to harass teammates, or death timer abuse to harass teammates, or really even spamming someone's item purchases to berate them for building wrong.
But god forbid I get trolled by a duo in Treeline and argue back with them, and get punished for that ONE game of bad chat behavior of retaliation, even though the majority of my games I am very positive or neutral.
Riot's punishment system is so heavily focused on chat-based flaming but ignores other forms of flaming.
Hell, I've even reported players for telling others to kill themselves, making race-based jokes, homophobic slurs, and no feedback on whether the person was punished or not.
But hey, it's more important to not argue with people than it is to not make personal threats, not spew hate speech, not demean others. I honestly think Riot's formula is to check a chat log flagged by a report, and just count the number of lines that the offending player has typed out in game. If they are "spamming" chat, the system deals out a punishment, but if the amount of chat entries they put out are at a minimum, no matter how toxic that minimal amount is, no punishment is dealt.