Cursive is wildly easier with a fountain pen. You don't know how much pressure a ball point requires and how much friction it has until you try a fountain pen. My "regular" handwriting is mostly legible but rather ugly. If I do cursive with a ball point it's nearly indecipherable (even to me). If I do cursive with a fountain pen it's legible and decent looking. If I take my time it'll almost look like the examples in the school books I had as a child.

It's a shame fountain pens are slightly too fiddly for every-day use since they still have some real advantages over more modern writing instruments. I've never had a fountain pen fail to produce a line unless out of ink. With ballpoints I feel like they don't work more often than they do.