Yeah I know it's supposedly "random" but both with the Raids and with Events where there are a range of different possible gear/salvage rewards potentially possible I REAAAAALLLLLLYYYYY wish they would introduce a kind of 'weighting system' whereby it looks at the number of pieces of each of the possible drop items that you already have and then weights the possibility of each one of them being awarded to you.
So then those items you LEAST NEED (i.e. have hundreds/thousands of) get their possibility of being awarded lowered and those you MOST NEED (i.e. you have 0 as they cannot be farmed and are only raid/event drop gear) get their possibilty of being awarded raised accordingly - I'm not saying 'guarantee us awesome gear drops' but at least weight the possibilities in such a way that there is a better chance of getting items you are short of since they are supposed to be "REWARDS" for doing well at a harder part of the game