This tendency to take stats, especially defensive "stats" that are pretty much worthless at isolating individual impacts, out of context is really frustrating, and it has only seemingly got worse since we got Kyrie.
This is literally like apples and oranges, folks. You're trying to compare the defensive impact of a guy (IT) that almost always played with two to three elite-level defenders to a guy (Kyrie) that may have had three above average defenders on his entire team. This gave IT much more help defensively, and it also allowed him to be hid more often on the D, which Kyrie didn't really get.
Furthermore, Cleveland legitimately did not care about defense, and that's not an exaggeration. They just were not focused on that side of the ball, because it didn't play into their strengths. Contrast that with Stevens' defense-first approach, and of course that's going to affect the comparison between starting guards.
Yeah, Kyrie has been a bad defender for most of his career; nobody is disputing that. However, unlike IT, Kyrie has all of the tools necessary to be an average or even a slightly above average defender, and we've actually seen him play high-level defense in the playoffs in their championship year, which is much more than you can say about IT. It's not any great leap of faith to suggest that Kyrie will be a much more reliable defender in our system that actually focuses on D and regularly utilizes high-level defenders (Smart, Horford, Morris, Hayward, Baynes, with hopefully Brown being added to that list this year).
Hell, by virtue of being 6-7 inches taller alone Kyrie is a much more dependable defender than IT. I understand the need to romanticize the past after such an emotional trade, but do people really not remember how bad IT's defense was all throughout the regular season and playoffs, especially the playoffs? He was picked on in every single series, and there was simply no covering for his defensive deficiencies. That's something that simply won't happen with Kyrie due to his excellent size at his position.
EDIT: Greece666 posted this Simmons quote on another thread, and I think it fits perfectly with what I'm saying here:
Isaiah, you know, in the Wizards series, again I love the guy, I'll defend him to the death, but the Wizards series, against Wall and Beal, was pretty eye-opening, they couldn't figure out who to play him on defense. Kyrie's not a stud on defense, but the Isaiah thing was a real problem, and I think Washington should have beat Boston in that series.