I wonder if @Stealthflanker can make an RCS analysis of this
Swept vertical stabilizers stall later and move the center of the yaw moment backward. This is why you see them on even ultra-light gliders. Trapezoid is less draggy except in transonic.It's a mystery to me too. Perhaps there is negligent RCS reduction gain compared to the drawback(s)? I can guess its heavier, and draggier?