Of my 10 placement games, I only won 4 of them.
In 1 win, our jungle was doing a great job of ganking and carrying. Our mid was doing pretty good too. In the 2nd win, it was the most balanced game I played during all 10. We ended up winning after a team fight, baron, and a good push. No single lane out shined the rest. Jung and mid at the most kill participation, and ganks were almost exclusively in mid and top. In the 3rd win, our mid hard carried the game. In the 4th win, our top was an unstoppable force wherever he went. Our jungle frequently ganked lanes. Our ADC did fine, but wasn't the main spotlight imho. Of those 4 wins, i got 3x S-, and an A- playing passive healer and mage support.
Of my 6 losses, we got absolutely stomped in 2 of them. Our mid was the only decent one in 2 of them with everyone else getting stomped. In 2, we were doing good, but then people got toxic, upset, and started throwing. Of those 6 losses, 5 of them were extremely toxic to the point where people started arguing more than playing, and in several cases throwing the game, regardless of whether we were winning or losing at the point of the argument taking place. Those losses were between B and C grades, playing passive healer and tanks.
I actually had 1 game where the jungle cleared bot farm mid/late game once, and our ADC got upset. Our ADC had the most cs when compared to anyone else in the game, and still claimed they needed it more than him. They both went for red, and our jungle got it, so our adc got upset, said they were inting, and ran down top. Ran past 2 waves and suicided to their top laner, then pretended like it wasn't intentional, saying they got caught.
I've played with people who had plat, gold and silver borders, and it seems that those I played with placed between Bronze I and Silver I. I'm not interested in looking up 80-90 different people to see what ranks they were in previous seasons, but I highly doubt it's just the plat players raging. I literally only had 1 game out of those 10 placements that were equal in skill, had no toxic chat, and had a friendly cross team convo going in all chat.