Well, I sort of share your views on the community at large (I've dealt with my fair share of toxic players on either side), and I'm sorry that you feel like the match(es) are more imprisonment than game. I'm also sorry that you had to deal with such a barrage of toxicity from all angles, too.
If it's any consolation, I imagine that your punishment will be a fairly light one. If you don't have a track record of leaving games (you mention this being your first time doing so, so I can only assume that's the case), you don't get any huge penalties off the bat. Probably a warning and a 20~minute LeaverBuster timer or something of the sort, but, outside that, you should be fine.
As for reporting a player and nothing happening - you don't really have any proof of that. Sure, maybe it just so happens that who you report doesn't get punished, but that's likely because they either had a bad game or made one, non-habitual slip-up. It happens, and the IFS is generally accommodating of that.
But, to say "nothing happens" is a little narrow-minded and pessimistic. Players who do flame, even if they don't immediately get sacked with a punishment, their accounts get flagged for further notice. Their toxicity can add up to a punishment if they have a habit of it, and there are even some cases where players immediately get a chat restriction because of a more-toxic-than-average match on their part.
I hope most of what I said helps you feel a little better, and maybe changes your perspective on the punishment system a little. And, once again, I lament your recent poor experience. Have a good day/night, Cycera.
