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