Shout out to anyone that remembers the Mushy Pea juggling shop in Manchester many years ago, where I learned all sorts of circus skills.
Unless you start throwing feathers or balloons, the latter requires you throw higher. That requires you to either spend more time launching them up (bad for the ‘decrease time between catching and throwing’) or use more force (bad for throwing accuracy.
Also, even assuming you juggle 4 balls keeping “time in hand” equal, you have to throw it higher by a factor of (4/3)². That’s almost 2.
And even if you manage to make those throws with the same accuracy in angles, the errors in location by the time you catch the balls scale by the same factor.
I think you might be thinking of 5 ball juggling.
4 ball juggling (or at least it's most common variant, "The Fountain" [0]) is fascinating because it's really juggling two balls in each hand in a way that makes it appear similar to the standard cascade. Though this may sound "less hard" than what people initially imagine, it's a very different feeling than all the basics you learn using only 3 balls.
That also forces you to have much more consistent throws which, as you note, gets harder because you also have to throw higher which scales up any error in the force you're applying.
Cascade pattern = easy difficulty
Shower pattern = normal difficulty
Box pattern = hard difficulty
I also juggle, and the result of the combination is that approximately every single person on Facebook has posted to me the video about solving cubes while juggling them...
Even sided cubes are the hardest because they have issues with "parity" that are only uncovered near the end of the solve and can be quite tedious to fix (at least imho).
But yeah, some people will be impressed just because it's bigger. They always say that it must be super hard. My stock reply: "It's like a jigsaw puzzle. Is 1000 piece harder than 500? Not really harder, it's just more of the same thing." Sometimes that gets a blank look, sometimes that induces enlightenment.
My favorite cuboid variant is a 3x3x4. That blows people's minds when they see it's not symmetric, and they handle it and realize that it can't do certain turns (the long axes have to be 180° not 90°), but in fact that limitation makes it easier and I can solve it almost as fast as a 3x3x3.
I would also say that this library covers more or less the “lower half” of solo ball juggling in terms of difficulty. With lower ball counts (say ≤ 4), there are a lot of these patterns that have complex arm movements and can be difficult to explain with words, so having such a listing with animations and step-by-step instructions is very valuable. Starting with 4 balls, there’s less and less time for moving your arms around and it is more about the sequence of heights of the throws, which are well described with just their numeric “siteswap” pattern and you can learn them just from knowing the number sequence. The site has only the most basic of those (e.g. 534) and even very common 4-ball (7531, 633) patterns are missing with hardly anything beyond that.
[1]: https://ianconvy.github.io/projects/other/libraryofjuggling/...
There wasn't much on YouTube at the time but I also think YouTube is a worse resource for pretty much all of these simple tricks. All you need is a slow loop to learn any ball juggling trick.
There was also a similar site that let you input siteswaps.
The noob gains once you get comfortable with 3 balls are addictive, compared to later patterns or tricks that can take hours, days or even weeks to pick up.
The rating is described as a rating "1 - 10"
But every trick is actually graded 2 to 9. ( https://libraryofjuggling.com/TricksByDifficulty.html )
Presumably no-one ever wanted to define a grade 1, just in case an easier one was discovered, and similarly for 10.
When I was learning to juggle, that was the first step - and for someone who's never really tried to juggle, or toss a ball up and down in a very consistent way, it's surprisingly hard. Honestly, probably not a 1 on the scale.
https://libraryofjuggling.com/Tricks/3balltricks/Factory.htm...
On the Box page, HalfBox is in a square frame on the top-right. If wikipedia were like this it would be unusable.