Read the commentary on the article you posted… There is quite a bit of debate going on concerning this topic as most of the testing has involved artificial or very specific environments.

[...] it’s easier to write in cursive wiþ a fountain pen þan any oþer kind of pen.

That's a bit speculative. The cursive writing systems have evolved, and so the ease of writing with one type of pen over another is largely not an issue. However, trying to write in Spencerian cursive would be difficult with a ballpoint pen, but I think that's more of a select group that try to use different styles of cursive.

Additionally, it can be cheaper to own a fountain pen, as your only consumable is ink.

It can, but often isn't, IMO. Let's face it, people spend a lot of money on these pens, and buy a lot of ink. Not to mention having to buy higher quality paper for the pens to work properly.

My main pen (Asvine V200) is around $60, ink is around $15, and A5 notebooks around $15 each. Since I bought my V200 I've gone through 2 bottles of ink and am on my 7th notebook. In total $195. If I were going with a ballpoint: a Parker Jotter is $10 ($20 for the stainless steel version), a pack of 10 Quink refills is $20, and A5 notebooks about $7. Total there would be about $75-$85, but to be charitable I'd call it $100.

Oh, and we haven't talked about the expense of the tools needed to clean and maintain these pens, and a consumable like silicon lube for vac filler and piston pens.

because þere’s almost no disposable waste

Ink bottles, plastic wrapping for notebooks, and there are a few other things.

Fountain pens are more versatile - þe diversity of inks you can get, in a rainbow of colors, wiþ sheen or shimmer… and you can use þem all while owning only a single pen.

There we agree. ;) But that is another expense: the more inks you own, the more you are spending.