The Argument
The Prequels added so much more to the world of Star Wars. They charted the background of one of the most iconic villains of all time, and showed how an aspiring hero became corrupted into the menace we know today. They expanded on the lore of the Jedi, showing them in all their glory and might, but also in their ignorance and arrogance that led to their downfall. They showed the social and political background that gave rise to both the Galactic Empire and the Rebel Alliance. The content in the Prequels gives Star Wars more substance, and makes the galaxy far, far away truly feel lived in.
What consideration did the Sequels afford to the world around its protagonists? Besides a one-off war profiteering reference, they didn't add much. The world (or worlds) of the Sequels act as little more than backdrops for the escapades of the heroes. The settings are mere stages for the plot, and the people are mere devices.
What's more, the content of the Sequels is essentially a rehash of the same basic beats of the original trilogy: an optimistic young Jedi turning a flawed villain against Palpatine. The Prequels had a much more original and daring story: a darker tale of tragedy and defeat. The Prequels not only innovated in terms of story, but also in terms of setting. They have an element of added substance that the Sequels lack.
Counter arguments
The "innovation" the Prequels introduced was terribly executed. Yes, they showed the story of Anakin Skywalker, but he was a thoroughly unlikable character who didn't resemble Darth Vader at all. Yes, they showed the politics of the Republic-turned-Empire, but it was boring and tedious; and was it really necessary in the first place? The Prequels added new things, but they messed up badly in doing so.
The Sequels added content to the Star Wars canon that was much better executed. Old Luke and Kylo Ren's arcs were both more compelling than Anakin's, and put unique spins on the original story formula. And new ways to use the Force are more interesting than trade deals. When it comes to innovation, the Sequels are superior.