You will never become very good if you blame WGT for your failures. The key to improving is to ask yourself "What did I do wrong?".
Very good point, but you should also not try to correct BS variance and you will encounter it without question... so the key is fix what you can and know the game will still give unlikely outcomes at times that you dont want to try and correct because they are outlier type variance shots that cant be fixed only managed with recovery shots.
The only way to try and discern the difference between the two is through reasonably good club ball charting.
Sorry, but I 100% disagree with you.
In principle, you may be right, but I doubt there are ANY new and few experienced average players that can "discern the difference". Additionally, the times when a bad shot is not your own fault is miniscule compared to the times that it is.
The above example of Merion #13 is the perfect example of why you should not blame WGT for your mistakes. Continue to play it the way you "think" it should play, continue to play it for the way your "clubs and ball is charted", and you will keep ending up in the back bunker. Accept that the shot plays different than how you think it should play, try something different, figure out a good way to play it, and you will never have a problem with that hole again.
As for "good club ball charting"... I have never charted a club or a ball. And although my game could use some improvement, I doubt it would help me.