The biggest advantage fountain pens have is physics.
Ink flow in a fountain pen is via capillary action (touch nib to paper, ink flows), as opposed to a ballpoint pen where you have to apply a small constant amount of downward force for the ball to have enough friction against the paper for the ball to roll. This might not seem like a big deal, but if you're writing a lot, it means that your wrist & hand will get much more fatigued with a ballpoint over time.
Put another way, ballpoints have absolute advantage over fountain pens, except for "sitting down and writing a lot."
Ink flow in a fountain pen is via capillary action (touch nib to paper, ink flows), as opposed to a ballpoint pen where you have to apply a small constant amount of downward force for the ball to have enough friction against the paper for the ball to roll. This might not seem like a big deal, but if you're writing a lot, it means that your wrist & hand will get much more fatigued with a ballpoint over time.
Put another way, ballpoints have absolute advantage over fountain pens, except for "sitting down and writing a lot."