RNG for upgrade items just doesn't work. There are always the unlucky ones vs the lucky ones and no way to compensate for the disparity. Even if you increase the drop rate, there is no guarantee that the unlucky ones will fare better.

I have killed the bosses in BoS over 30 times and have only received one storm cell. At this rate it will be the middle of June before I can upgrade my first bought piece. A drop piece is a waste since the idea of upgrading that would be impossible. I know of people who can give the same tale for tenebrean engines.

It is time to make them more accessible. Possible ways to do this is to let us buy them with raid currency, give a chance for them to drop in the personal loot bag in raid rifts, or give a chance for one to drop after boss kills that the raid can roll on or distribute thru master loot. In fact, at one time the last day of the pop up calendar gave us a slight chance to get upgrade items.