I don't think the games you listed are very intensive on GPU. The Witcher 3 might be demanding on high settings, but it actually does not cause much heat, in my experience. I used to play Dark Souls 3 and Witcher 3 around the same time. My GPU temp never went above 80 even after playing TW3 for half a day, while DS3 always pushed it to ~90.
It's hard to tell, since not every game just crashes when the graphic card starts to throttle. When I play TW3 or some other newer games my FPS would go down after a bit because of the throttling, but they never crash. In the past, forcing the GPU fan to run at max speed helped me deal with this problem.
Anyway, the best way to verify this is to get an utility that lets you check the temperature of your CPU and GPU. Check your temps after playing this game and maybe some other games for half an hour or so. If they are too high, you might indeed be dealing with an overheating problem.