1: Git Gud. The racing at higher license levels is really good most of the time, I have been involved in some of the best races I have ever had on GT Sport. Part of getting good is developing situational awareness and learning defensive driving skills while racing. It takes practice but often you can learn to read bad drivers and avoid them. There are plenty of websites devoted to safe racing and driver development but the Surviving Rookies series on Youtube specifically made for iRacing might be a good place to start as much of the advice carries over. I will add one change though. In GT Sport it is still important to try and achieve the best finishing result you can but first focus on your SR rather than aggressively going for positions. Sometimes it is better to let "that" guy past as clean as possible.
2: Was he driving a Megane? Maybe it wasn't intentional. Earlier today I watched a Megane driver wreck everyone in my sons rear vision mirror as he started his race, I was sure he was just trying to wreck people on purpose. Then he kind of disappeared for a while before he reappeared in my sons mirror gaining on him quickly. And in most corners he would take himself out into a wall even when there were no other cars around him, it was at that point I started to suspect he was just a very bad driver. And yet he kept on catching my son. I could not believe what I was seeing, this guy was not making corners, he was crashing into walls and yet on the straight he was so much quicker than everyone else. When I saw him approaching my son I told my son to get out of the way and let him past. And he blew by, his pace was incredible on the straights especially considering his corner exits were terrible. Shortly after he took out the car who was in front of my son which allowed my son to gain that position and he got by one more car to finish 2 places ahead of my son. After the race the first thing my son did was buy the Megane and in his first lap he ran two and a half seconds faster than his previous personal best. During that race where that Megane wrecked lots of drivers, my son gained 6 positions and he went from SR:A to SR:S in the Evo Gr4.