I am told that my handwriting is pretty good, so I can't say with certainty that this hobby will be life-changing for people whose handwriting is illegible. But! I do think success has a lot to do with simply following the tutorials and practicing regularly, and speed, rhythm, pressure, and muscle memory definitely play a big role. So I wouldn't count yourself out just because you write like a third-grader.
Envelope Address Hand Lettering Tutorial from Ladyfingers Letterpress
Making all of those slowwwwww loops up and applying juuuust the right amount of pressure on the downstroke feels really satisfying. For me, it's been a nice way to unplug and sort of clear my brain at night.