> you either have to decrease the time between catching a ball and throwing it again or increase the time a ball is in the air

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.

0. https://en.wikipedia.org/wiki/Fountain_(juggling)

They're not wrong. Assuming alternating hands are doing the throwing (rather than both hands throwing a ball simultaneously), 4-ball patterns mean each ball is in the air for 4 beats, while 3-ball patterns only take 3 beats each.

And once one realises that many juggling patterns can be understood by the number of beats each ball takes to return to a hand, one can then think in siteswap (https://juggle.fandom.com/wiki/Siteswap).