So to preface this counterargument, I have been to every ELO except mid-high challenger. I have been in challenger twice totaling 4 days. I can tell you this, you are completely and utterly incorrect about not only that mood is everything, but the reason you lost that game. Do you know how many players get into Diamond+ being completely negative? Alot, a hell of alot.
So onto the first point here. Alot of challengers have issues in Silver, and I can tell you this, it isnt due to toxicity. There is an extreme matchmaking issue in the game currently at low elo that ends up making games unwinnable for people who have decent win rates because... reasons? I will tell you this, there are players ranging from Bronze 5 to Master tier players in the Silver - Gold ELO range. The game seems to pit itself against good players who are climbing fast, or against duos. And what I mean by this, is the enemy team will get an LCS comp, and we will get a Vayne adc. Do you know what the problem with this is? Not only does the enemy trist just outscale your vayne, but beats the vayne early. There is 0 reason to play vayne in silver unless you have god tier mechanics, which im sorry but you guys dont. Just play Trist, Kog, Twitch... Any of the three really. The more interesting fact, is that in the game you are talking about, if the adc picks Trist, its an autowin. Instead chose to pick Vayne and take a tumble into an inevitable loss provided the enemy team just plays well, which they did.
Picks matter, doesn't matter the elo, they do matter. And if you continue to pick things like Malphite and Trynd jungle, you will keep losing games.
The other problem in silver, is not the toxicity itself, but the people who cant click the mute button, that is specifically there to prevent tilt. As soon as someone is toxic in my game i just mute. It is that simple, I havent reported someone for toxicity in forever because they might just be having a bad day and need a way to vent, and if i dont want to see their text i have a button that removes it. The common trait i see in toxic players is their ability to play well while tilted. So if all 4 of you muted him the game would have went unphased. Instead you come to forums to cry because you forgot that the mute button exists.
Just keep this in mind: Just because a pick is popular in low elo, doesn't mean it is good. Mute toxic teammates or don't cry about it. There are much bigger problems than someone in your game crying their arse off about vayne being bad, like matchmaking being completely flawed, or the report system banning people for talking a bit of crap to inting teammates, or the fact you can get away with literally intentionally feeding but just say you are trying.
Execution and Skill are the two main factors of league and always will be. If you are so weak minded to be thrown off by someone crying about a champion, perhaps you should take a break from the game because clearly it is too much for you. You cannot decide that the game is lost (because someone is crying in chat), and then blame it on them, you decided it was lost :P