I'd say the level of quality was pretty much the same with Ranieri's defense. It was a zonal defense, as you mentioned we played tightly with the midfield contributing to its success at times. From my experience playing a zonal defense it works if you have somewhat competent fullbacks and players with some level of football intelligence, which we apparently don't have judging by all the times these attackers get behind Gryger, Grosso, et cetera. They don't even know what it means to remain goalside of an attacker. So the CB's have to get sucked out and that destroys the competency of the zonal back four.
And as we have seen on some set piece situations, some of these guys can't mark anyway, so the man to man setup wouldn't save us either.