That's not really accurate. It's difficult to imagine mow because they're so dominant and they're the only Itaian team these days who threaten to do anything in Europe, but they 'struggled' for a while. They got promoted in 2007, finished 3rd, 2nd, 7th and 7th. Even in 2012 when they did finally win Serie A again, it was a close run thing and if memory serves I think it even went to the final day against Milan.
Conte (along with the neccessary good club management, new stadium and excellent transfers) made them the unchallengeable behemoth they now appear to be. They struggled to get back on top. He was huge for them.
I mean it helps when Milan and Inter went to shit but Napoli and Roma you could argue filled that gap anyway. Napoli provided huge competition until the final weeks of the season last year, for a long time looking the favourites.