I think the most effective layout is to have Library and Project bin in one place, switchable using tabs. However, Library has buttons located at the bottom, while Project Bin buttons are at the top. It would be more logical to unify it, either have both buttons located at the top or at the button. Top is probably better. Reproducible: Always
To me it makes sense to have the buttons at the bottom of the library widget because it is closer to the timeline, which is the situation where you most likely would use it.