The last two times I've pulled for monster shoulder pieces, I've blown a total of 140 keys, and I still haven't pulled the armor weight of the shoulder pieces I need. To be more specific, I blew 85 keys trying to get Earth Gore Epaulets (light armor), which was the last remaining piece I didn't have from the monster set. That's 17 pulls to try to get one specific shoulder armor piece (I had the heavy and the medium Earth Gore pieces and all the Domihaus shoulder pieces), and I did not get it.
Fast forward to this weekend, I blew another 60 (or more) keys trying to get Engine Guardian Epaulets (light). I had both the heavy and the medium shoulder pieces for Engine Guardian, and all the shoulder pieces for Sentinal of Rkangthmz, so surely I could get ONE of the shoulder pieces I needed in 12 pulls? Nope. All 60 of my keys blown, with nothing to shown for it.
Now I loved the change from the system where you spent 1 key to get a totally RNG pull for shoulders - and it could be from ANY of the dungeons that Pledgemaster offered - to the current system where you have 5 keys, and you can narrow your selection to try to get a piece from just a handfull of dungeons, but the RNG is ridiculously bad, and it completely wastes the player's effort made in grinding out all those keys. A couple of things that need improvement here, IMO are:
1. Curated drops for shoulder pieces (i.e., apply the smart loot system to Shoulder Pieces so RNG is weighted towards you getting the pieces you are missing);
2. Increase number of keys awarded for Vet Dungeon HM. It's only ONE additional key, and depending on which dungeon it is, the increased difficulty is not worth the extra key. Perhaps each dungeon should have a difficulty rating where the number of keys awarded for a hard mode completion (2) is multiplied by the difficulty rating so the extra effort is more greatly rewarded.
3. Have a separate "golden" vendor tied to the Undaunted that will allow you to purchase shoulders for gold on the weekends. I know the Golden already does this, but its random whether she has helmets or shoulders, and if your looking on that particular shoulder piece to perfect your build and you've had crap RNG in pulling shoulders (like I have), this gives you an additional chance at getting what you want.
4. Lower the price of the boxes to just 2 keys per pull. That gives you 3 chances per day if you do all 3 Vet Pledges on HM to get what you want (per character of course); or
5. More undaunted-related events that give you exponentially more keys for Pledge completions and your first random.
Bottom line is that I just think it is complete crap that it takes so much time to accumulate enough keys to make a number of pulls to give you a good chance to get what you want - only to not get what you want. That's a complete devaluation of my time as a player, and IMO, this should really be addressed, if not by one of the four ways suggested above, then another way that makes it easier (not necessarily easy, just easier) for you to get what you need. 30+ pulls to try to get 2 shoulder pieces you're looking for, only to wind up with NONE is just unacceptable.