Apparently, however, that figure still "eclipsed the numbers from the end of season 4."
And, right or wrong, that eight million figure still means its more popular than most of the rest of the shows that people here -including myself-enjoy.
Well, no. It's down 400K viewers (scroll down to end of S4, start of S5). That said, it's better than the penultimate episode, ratings ticked back up again, and overall not significant enough to be a worry for the show.
For comparisons with a few shows that get regularly talked about here, Castle averages between 9 and 11 million viewers, Once Upon a Time between 6 and 8, SHIELD 6-7, The Walking Dead 12-13, and How I Met Your Mother 7-9.
So Duck Dynasty's certainly very impressive (and like TWD a cable show rather than a major network) but it's not massively more successful.