lol i think you are looking wayyyy to deep into this...the mount is fine...u are assuming if i use it, then it will just lift up my car and i will go flying away...seeing as tons of cars have used one just like this...im not worriedBecause levers. You attached a giant lever to the back of your car and you're going to pull on it hard at speed. You should at least do some rough calculations before you just stick stuff on and call it good. Especially if you're going to use it in a racing environment.
Your assumption about lifting the rear is at least partially incorrect. It'll act like that if the parachute is directly attached to the back of the car. You didn't do that here. You attached a lever to the bottom of your car and put a parachute on it. Completely different system with additional moments and forces.
Also, the rear brakes are fraction of the size of the front ones. It's a very strange assumption that the rears will make up for the fronts in any meaningful way.