I can see how you might think that Trigga.. but the converse seems to be the case.
All the owner of the rifles I've added this type of system to have reported INCREASED accuracy. Their opinions on this, as well as pretty extensive testing by yours truly, seem to be with the change in recoil characteristics. It often does soften subjective recoil.
The thing to remember is that with piston drives you achieve kind of a "pushme-pullya" energy transfer.
Explanation: When the bullet travels down barrel the piston , after the bullet passes the gas hole, travels to the rear of the weapon. This tends to balance the forces engendered. What that means in real world terms is that it shortens the time needed to get back on target by limiting muzzle rise. Now granted a good muzzle brake will do that too but, this type of system does it while the bullet is still in the barrel. Not after it's left it.
This characteristic is one of the reasons piston drives have become so popular with 3-gunners.