There are more solutions than two that deal with reducing gas.
Increasing mass of the moving weight of the parts that cycle or increasing spring tension that fights the movement of the mass.
Increase the mass of the group too much or spring tension too much and the gun will not operate without the silencer.
Increase the spring tension too much without increasing mass of the group can result in cycle speeds in the closing direction too fast the a magazine can not feed fast enough and bolt carrier bounce open can be excessive.
Get the mix just right and there is not need for adjustable gas system.