A four stroke exhaust can be designed to resonate at a frequency which helps clear the spent charge and allow the fresh charge in, by forming a low pressure region at the port. This is to do with the mass and inertia of the pulsing gas flow. I relate this to a trombone, which can be altered in length to play different notes. As someone has already pointed out, there is no exhaust that will give extra performance right through from idle to maximum rpm, except a more freely flowing one, compared to a quieter but more restrictive one.
A two stroke engine has much more rapid opening of its "valves", which are in fact open ports opened by the rapidly moving piston skirts, rather than cams, which open far less suddenly due to their design. This more rapid opening results in an additional exhaust pulse, a sonic one, which can be further exploited by "tuning" the exhaust design to help "pull" in the next charge of mixture. So two strokes respond better to tuned exhausts than 4 strokes do.
However, I would have though that because an aircraft piston engine operates within a fairly narrow rpm band, there would be some scope for exhaust tuning.