Would you say that the juggernaut update was a success seeing as Garen's, Morde's, Skarner's and Darius' ban rate skyrocketed?

The ban rates are less than optimal, to be sure, but they're largely overreactions, I think. Our data show that many of the most banned champions really didn't perform that well in game, especially not after follow-up nerfs that brought their win-rate, but not their ban-rate, down. The player base as a whole is slow to react to changes in the ecosystem.
From a pure design perspective, yes, I absolutely think the Juggernaut update was a huge success. It's a statement of intent and of what we can do, as a design department: we don't have to bow to the fact that a lot of our old champions have ill-defined gameplay and are kind of dumb to play against. We can apply our understanding of the game and fix that shit. Yeah, we'll break some stuff in the process, but that's easily fixed. Compare today's Gangplank, Darius, Garen, and Mordekaiser to what we had before the juggernaut update. I think it's really obvious that the game has become better in a meaningful and lasting way.