Remember that chance based drop systems are completely unpredictable. Even with an item drop rate of 99% you might be extremely unlucky and not get the drop. No matter how many times you repeat it's the same randomized drop result. This is the pain of these systems, especially with content that takes more time. On some characters, you may run BM, Garg and Alch (for different drops) 2 times, or 50 times before getting a drop. It isn't 'fair' but I can't think of a better system.
However, perhaps an improvement is possible (I have no idea if it can be done), by store the last drop of a boss and increasing the chance of dropping the other items on the drop table instead. So that for instance BM keeps dropping Turban 3 times in a row, but then it's drop chance is down to 5% making other drops more likely.
I think such a system is very hard to make though, cause you have to store a lot of data throughout a game and not only for 1 boss, but for all. Also, what happens when an item dropped a lot "early on" but then doesn't drop for a long period of time? Perhaps for each time an item doesn't drop, increase it's drop chance up to a certain point.
But by now, Zwiebelchen has surely thought through all different systems and found that the current one is the best. So all of this is just pure brainstorming.