Q: Is the lower ball joint on the driver's side fixed as one part with suspension arm or detachable?

Hello. The ball joint is available separately, and as part of the control arm assembly as you note. Although it can be purchased separately, removing it and replacing it into the control arm requires heavy duty presses and tooling (great force required). And if the control arm is aluminum, it is a more risky process since the aluminum is softer than steel, and the remove/replace process may not result in the ball joint fitting as tightly in the control arm as would be safe. For the mechanic, sometimes the separate ball joint is not readily available, only the control arm with ball joint. And the labor time to press out the old, press in the new may result in a more expensive repair anyway because of the additional labor cost. It’s a toss up sometimes, especially with parts availability being a deciding factor.