(okay, yes, also the inks themselves were completely different, with fountain pens having to use dyed water solutions to avoid clogging the pen, whereas dip pen inks actually have solid particles of pigment held in suspension in their ink, giving bolder colors and darker blacks when dry on the page; if you put a dip pen's ink in a fountain pen it would very quickly clog up with those pigment particles. And back in the day, it would probably eat right through the latex bladders the ink was stored in)
The fountain pens you get today are very different from the ones back then; they have stiff nibs which can survive the sorts of pressures that ballpoint users are used to inflicting on their pens, and they're equipped with quick-drying ink. They're pretty much indestructable under normal usage. But back in the day a fountain pen required a very light touch and some patience (or blotting paper) to ensure the writing didn't smudge and that you didn't damage the nib.
(there's been a mild resurgence in the popularity of flex nibs in fountain pens over the past few years. I haven't seen any which have anything like the flexibility you see in real vintage pens, but it's a lot more than we've seen in fifty years and it's nice to see them making a modest return!)
Nowadays, when I write by hand, it is always in haste, standing awkwardly in front of some flat surface, and using a scrap of paper and a partial dried-out pen I got for free a decade or more ago. No wonder my writing has gotten worse! And it wasn't good to begin with.
Now that I'm thinking about it, I've not kept the preparatory aspects of good writing from the past when I am "writing" on my computer. The keyboard is always there, a fresh "sheet of paper" always at hand, and it is so easy to edit and change my writing afterward, that I don't care much about thinking before writing.