Echo Knight dropping all items, makes him entirely mandatory to farm, but at the cost of not doing anything else.
Each boss should have a specific loot table and they need to drop their unique loot, and only those. Echo Knight, could have his own loot table or be associated with other things like specific rare upgrading materials or whatever but he should NOT be dropping all loot.
Farak-like boss, or canonically, other high ranking members of his “gang”, should be able to be encountered in the wild and drop his own loot.
Spread the uniques over in the entire game, because if you keep all the loot in the Crucible, then we are going down the path of Diablo, where there is really only 1 thing to do again.