The loot system is not gambling, calculated return in long term based on gear, skills, choice's.
But there are gambling / luck element's like:
The same mob gives shrap, oil and esi, etc and other common stuff for all, but 1 get M91 Stalker Augmented, that drop have nothing to do with gear, skills, just pure luck.
Boxes, you can open K's of them without seasonal ring, while somebody get a Halloween 2019 ring from his first ever halloween box.
Ofc the more you open the more chance you will have to get one, and that is the reason why ubers get a lot of them, they open much more than others, but this is partly gambling.
Mayhem competition's with the 5k score's are also luck based, so partly gambling, where the better gear and bigger bankroll have advantege, but this is also gambling.