You, quite literally, don’t understand the gambler’s fallacy.
The possibility of that guy being on your team is included in the typical behavior of a dice at your rank. Everyone has to play with the same dice (except for their own).
No argument here. Trolls, leavers, boosters, etc. are bad for the game play experience.
Since you are not posting from your game play account, I couldn’t see your rank. LFG does tend to break for the higher ranks. The question is why? Games are more fun as a group, there is an SR advantage (Groups and Matchmaking in Overwatch, unlike early in the history of the game). The only real problem is one of population: not very many people are on-line at your rank. But this could be overcome with greater organization. Maintaining friends lists, planned play times, using LFG to fill out holes in your comp and expand your friends list, etc.
I know it’s a lot of work, but Masters+ is the top of the ladder. Shouldn’t players there be willing to put in extra effort to get a better experience?