I wouldn't call it stupid, I would call it "inefficient design". What kind of design is purposefully having to replay the exact same fight an indefinite amount of times depending on luck? Now replaying it and getting at least a minimum guaranteed amount every time makes sense because worst case scenario you figure out the minimum and work out how many times you need to kill it to get the items you want. The chance of getting nothing adds no difficulty whatsoever at a time expense of not only fighting the boss again but also farming the materials of the previous spawner, usually leading to refighting bosses that have long become obsolete because of item progression.
These items should either: Drop every time in large amounts, to only have to fight the boss until you can beat it (like the base game does, and also make the bosses harder in this case so the item's value doesn't drop) or drop it every time in tiny amounts if you really want players to farm constantly and fight the same fight several times in a row.
The idea I had of bosses dropping their next tier items only in their specific biomes is a good one. Fight by their rules or get nothing. But I figure tApi doesn't have those tools yet.