That is not a good criterion. If the horizontal toolbar did not flicker, why not use that one? Also imagine that you are allowed to remove the text in the horizontal toolbar so that it is neater. The issue with the bloated gui is that its hard to make fixes (the code is messy). And logically speaking, instead of having 10 incomplete features, why not just offer one that works well?
And giving every possible option to the user is not the ultimate goal: if this were the goal, the toolbar should be able to be positioned at the botton, on the right, diagonally, it should allow you to reposition its tool buttons, to eliminate some etc. Why aren't those options offered? If those options are not offered what is the problem with removing one more similar option? The toolbar orientation is not central to the function of amule, which is to download files, and simplifying the code helps identifying bugs and improving the relevant functinality.
I guess once an irrelevant feature enters the code base it is very difficult to remove it in the feature and I am sure developer's ego plays (an admittedly very understandable) role in that. It's kind of sad to think like this...