No. That is not correct. Instead of being combative and argumentative, you might take a minute to learn something from the link that you posted yourself. Grade 5 is specified for brakes, towing, suspension, and other applications for the toughness of the material. The grade 8, as you can see in the graph you posted yourself, breaks suddenly, and without deformation. The grade 5 has a long yield curve. Now it's not only important to be able to read and understand that graph, but it's important to understand why manufacturers who are subject to liability lawsuits for the products that they make, would specify the grade 5. The grade 8 only retains it's superior strength if the bolt in question is torqued properly, for the life of the fastener. That is key to understand. Through the life of a fastener, use cycles, heat cycles and corrosion, bolts lose their torque. When this happens, they fail. Grade 8 fail in a catastrophic manner, whereas grade 5 provide warning. Your brake bracket will still be attached to your axle, or your trailer hitch will still be attached to your frame.
Go ahead. Look at these components and see if they are not put together with grade 5 bolts. I'm not just making this **** up. I have a degree in Mechanical Engineering and I actually read manuals when I install aftermarket brakes on my trailer, or my trailer hitch on my vehicles. Grade 5 are used for their ability to yield slowly and not catastrophically fail.