What in the world.. how did you even come to this conclusion? They're literally both fictional wings. Not one person is bragging about it, so I'm not sure why you'd bring it up as if someone was. I'll give you that Forza's isn't the best looking, however, it's also not the only option for many, many cars. GTS doesn't even allow you the option to change any thing aesthetically, besides the rims. So having an option to do that is better than not.
GTS is not the only one to start from the ground up, and regardless of that, that doesn't eliminate any issues anyways as
@fatkid has put some perspective on it as well with these posts
Starting from the ground up is a nice thing to do, especially when working with content that came from the last generation of consoles. I'm glad that Forza and Gran Turismo have taken this step.
As for Quantity from Forza 6 to Forza 7, there is literally a couple hundred more cars added into it since then. Quality being the same as Forza 6 is in no way a bad thing, as quality was already there in the first place.