I get no controller or sound latency.
You may believe that, but it is impossible.
On an Amiga you can change the display in realtime, so you could change one of the palette colours or play a sound and then read the joystick on every scan line and instantly change another palette colour or play another sound.
With usb the default polling rate is 125hz, you can increase it but I'm not aware that winuae reads the state more often than every screen refresh anyway.
It is very difficult to keep the sound and video synchronised because of latency in the drivers and lcd monitor. You only present an entire frame of video or audio at a time, so there will always be some form of latency.
You might not notice, but it is there. Some people perceive it stronger than others.