Don't let the example picked by that user fool you: that's not "medieval handwriting" as such. It is a particular type of medieval handwriting, known as Gothic textualis, that developed in the late Middle Ages. It was used almost exclusively for luxury manuscripts like the one shown--large, colorful, even decorated with gold leaf in this particular case. It's from a 15th century prayer book of standardized prayers that would have been specially commissioned by a wealthy noble, probably a woman, more for use as a material component to guide meditation, and for display, than to actually read in the sense of obtaining new information.

For a contemporary comparison, here's a mid-15th century compilation of original prayers and lessons that would have been newer to a reader, rather than something memorized. This one, you might note, is in vernacular (here German) while the prior is in Latin--this one was meant to be read and understood. The physical codex is smaller; it's to be held in the hand, not propped up on display.

Gothic textualis didn't come out of nowhere. The fancy half-line-sized minims with barely visible horizontal lines that pretty much look like the serifs so everything could be mu or nmi or onni is the result of centuries of evolution. Here's a 13th century version where Gothic textualis is emerging out of what scholars for lack of imagination call "proto-Gothic", again, from a lavish luxury manuscript. Much easier to make out the letters here, to modern eyes, right? And a step further backwards in time, here's 12th century proto-Gothic, which appears even clearer to us.

That early early proto-Gothic is just starting to get a bit spikier and have heavier serifs than the hand (font) it will eventually replace, miniscule/Carolingian miniscule. Here's a late example, from an 11th century Bible, and here an 11th century prayer book. We're tracing a change in style and artistic quality, not desired legibility.

No, workaday manuscripts--personal devotional booklets of prayers and lessons compiled by their owners (or passed down from, typically, mother to daughter), legal records, letters, and academic textbooks--can get extremely messy. I gave you a really nice example of Gothic cursiva up above. Here's one that's a little more fun.

As for the abbreviations: again, the user in the other thread is being a little cursory with their remarks. (I stress they are not wrong. At all. Just telling only the part of the story relevant to their point, which is fine.) Yes, heavens yes, medieval scribes had a million zillion abbreviations developed over the course of...a millennium. However, for a manuscript like--again--that one meant for show, there was a set of common ones for common words and endings. A lot like we recognize "won't" is "will not", even though the "o" comes out of nowhere. These are consistent even when the Latin word is borrowed into the vernacular, which is fascinating. Remember, people are writing out every word of these by hand, and books are still extraordinarily expensive. (By the 15th century, booklets and pamphlets, less so.) Time and space are both very precious. It's really in bureaucracy documents and in manuscripts coming out of a university context that we see the really crazy density of abbrevations. Capelli is your friend.

Medieval people developed a lot of ways to keep written information away from prying eyes of unwanted readers: destruction of texts, tearing away title pages and first pages so the book would seem uninteresting or like something it wasn't, the use of Latin instead of the vernacular to restrict the audience to clerics and other religious (i.e. people who took vows), and most importantly, simply not committing a message to parchment or paper in the first place. But fancy, show-off handwriting was not one of them.