You might think that, but in fact it's the opposite.
An engine has to do more adjusting when the back pressure is consistent all the time.
This is how I understand it, plz correct me if I am wrong here.
An engine's top end performance is best when it breathes freely.
So straight pipes give the best top end performance.
However, they create idle/low end problems.
The tailgunner gives you that backpressure until it starts to spin. Once spinning the back pressure is reduced the exhaust flows freely. Best of both worlds. While traditional exhausts with a fixed back pressure are tuned to a happy medium.