Everything isn't doubled, but yes, there are 12 models that are repeated in the boosters (so 36 unique models, and then 12 more for a total of 48 if you buy one of everything)
It feels a bit cheap but I think it works quite well, especially if you are the only one in your group who owns it so that you draft every time. Then there are options for several players to use those models.
Some of the duplicates feel suboptimal though, 2 December Acolytes, really?
While some, like the Bayou Gremlin who really needs bro's to shine, aren't duplicated.