You highlighting the language issue is interesting because it makes the assumption that one can get the line width they'd like from a ballpoint pen, which personally, I didn't. Ultimately you need to choose what works best for you, and the language you write in is certainly a consideration. I'd much rather have the option, than be stuck with "one size fits all" of most ballpoints. So saying that's a con is a misnomer for me.
All that being said, a fountain pen is not a tool for every use case. I was a lot happier when I realized that a ballpoint or rollerball is far better suited for tossing in a bag or having at the ready when traveling.