Yoiu are all not seeing what i mean. The lower arm is attached by a ballljoint yes. In Formula 1 the knuckle is designed to take the weight there. In the case of all the cars used to build this car the shock and spring is normally standard in the top of this knuckle. The just look and the size difference in the metal between the top and the bottom of the knuckle. On the kit cars the rolls the parts have to play are reversed.
Think about it the lower ball joint has the whole weight of the car and have to contend with the spring and shock stopping it from giving on bumps while the upper arm moves freely and just follows the knuckle.
Are these lower joints as a question common for replacing on mots by any chance? Bet the upper on ain't so prone to it.