Most and perhaps the only important part of the booster pack content distribution is about the highest rarity cards because by the time you get all play set of the highest rarity card, you will have enough copies for the lower rarity cards. So what’s the HEX’s distribution for legendary cards?
Primal Pack: 2%
In the Set 1, there are total of 23 legendary and 106 rares. Assuming no duplicate, which obviously is impossible by statistics, you need total of 23 x 9 x 4 = 828 booster packs.
The legendary is not included in this calculation, which would decrease overall number but should not be by much. Each primal pack contains 2 legendary.
Since HEX has auction house system between players, no sane player will just buy booster packs to complete the set. Therefore, don’t assume this is the actual cost for set completion.