If you do Marduk you can get 10-12 relics per hour (4-5 minutes). This is split up between 8 Axi and 8 Neo relics, and only two of those relics are the unvaulted relics. You have a 6.25% chance of getting either a neo or unvaulted relic if all relics have the same drop rate. If I did my math correct, and I did not because I'm terrible at math, it can take about an hour to an hour and a half (depending on how speedy you are) to get one unvaulted relic from Marduk.

You need to get at least 6 Axi relics (you need two Bo Prime ornaments) to get all the rewards, and since the rewards are split between neo and axi, you'll need to play at least 12 hours to get those 6 Axi relics. Of course you're not going to get all 6 items from just 6 Axi relics, so you'll be playing a shitload more than that to get everything.

From this, we can determine they don't intend for us to farm Axi relics, but instead buy the parts from other players. While it's very unlikely any particular person will get a needed drop from a relic, there's so many people playing that these parts are constantly dropping for the community as a whole. An unvaulted neo/axi relic will drop approximately every 14 runs of Marduk, and there's hundreds of thousands of players. If 100,000 players run Marduk one time then we would expect about 7,140 neo/axi unvaulted relics dropping.