It's very difficult to bend a factory arm unless you land one of them hard on a rock... which could bend an aftermarket arm too. The factory arms are actually a better design that is more flexible than many aftermarket designs are. They can twist when needed, like when the axle is twisted up on an uneven trail. Not all aftermarket arms do that nearly as well. The factory design is better than many would suspect.
After replacing my factory arms with Tera's first-generation control arms that had rubber bushings at both ends, it wasn't long before I had one, then another, control arm mounting bracket tear off where it was welded to the axle.
So whether it's a good idea or not to swap your factory control arms for something else depends on the aftermarket arm. Some are worth it, some would be a bad idea.