Ultimately the point here is that you're just being a hypocritical whiner. Saying the GT is not legal for the class if laughable bullshit, and if you believe that bullshit when you say that, that means logically you have to believe the rest of the class is "illegal" for the class as well. The GT road car is by far the most similar car to it's race car variant in the GTE/LM racing.
The other manufacturer's cars were not built solely for racing in that class. They are road cars adapted for the track. Ford built the GT SPECIFICALLY for the class and still needs to skirt the rules to compete.
The difference goes beyond the minor items you listed.