I just don't particularly understand why loot is this way currently. I personally stopped playing because honestly chasing a build was taking long periods of time to get any piece because there was no real way for me to chase anything specific and my luck feels extra trash even running 90 luck. I recall spending about a week and a half trying for the life of me to get a mw component for ranger as well as I still have never seen a last argument or a single mw light machine gun which were my favorite weapons all the way up to when I started gm1.
I just sincerely hope the team understands the problem. I can't speak for everyone but for me getting anything I want feels unattainable and ending a mission with a barren rewards screen after I salvaged everything is about the worst I've felt in these types of games.
As a comparison in td2 I'll run around for an hour or two and then have to pick through my inventory to clean it out after all 100 slots of my inventory fill. It's certainly not all good but I'll walk away with a generous amount to tinker with and it's enough that I can keep chasing for the perfect piece. That alongside recalibration really lets me feel like creating my perfect build is attainable.
I think we understand what some of the core issues are... there's a huge problem with variance for example... with a large enough sample "everything is working fine". But the issue there is that that isn't the case for people actually playing the game... you don't get thousands of drops in a night for example - so statistics aren't really comforting there.
So longer term fixes to the base system will likely include reducing variance and narrowing the band between "lucky" and "unlucky" people.