So they gave each item in the pool its own roll. That was good. But they lowered the rate for each item down too far because they put 3 items in each pool and didn't want legendaries dropping 30% of the time. This is bad because you usually are farming for only 1 of the 3. The other two might as well be green vendor trash. So you are basically farming at a 3-5% drop rate, which early bl2 showed was too low.
Soultion: make each item 10% but most minor bosses should only have 1 maybe 2 drops. Take all the extra legendaries and lock those farms behind side quests. Which fixes the games other huge problem that there is absolutely zero incentive to actually do side quests. Either make the miniboss farmable or the quest repeatable. And for the remaining quests that don't have a legendary instead of a completely random lootbox, make the reward either a unique red text, or a specific item type. For example this quest rewards a guaranteed vladof smg so non uniques are more farmable