That's what's so funny about your rant.
You say it needs to be perfect, your a perfectionist, and Gran Turismo should be perfect.
That alone is ridiculous and in itself unrealistic. Welcome to the real world where nothing is perfect.
Second, if you had spent any real time track side, you would know different teams using the same car will do things differently. One team with a GTR may fabricate a fancy heat shield making it blend into the styling of the car immaculately, while another team with a GTR may just slap on metallic reflective tape around it where they feel it's needed.
Weather or not you feel PD used a stylish option is a matter of opinion and irrelevant. There is nothing wrong with it, It's supposed to be there. There is nothing to fix. It's like saying "the Evo is broken since I did a Racing conversion because it's got a wide body kit that doesn't look good, PD should fix it" because in my opinion they should of used a better looking wide body kit.
It's not smart to look at something that is a matter of opinion as something to be fixed to your individual liking.
The fact of the matter is, there is nothing to fix with the GTR's exhaust wether you like it or not, & if you were the perfectionist you claim to be rather someone on a childish rant then you would be more concerned and consumed by the many real imperfections with the game.