They are plenty durable. They're both strong AND weak where they need to be. Guess what happens to your solid aftermarket control arm when you strike a curb...
Nothing. That's the problem.
As far as stiffening the stock arm for track purposes, there's reinforcement kits you can weld on. basically consists of a few sheets of metal you weld on. bracing.
Seems like you just want to buy it for the sake of having it. Totally unnecessary and the stock arms are 100x better IMO than any aftermarket junk.