My own experience - a good length & design silencer does improve accuracy
Been playing paintball woodsball in particular. Markers currently owned X7 and SP1. They do not have silencer. But there is an underlying theory to holes on the barrel few inches before the paint exit the barrel. It so that the pressure behind the ball is gradually equalised. I do find ported barrels to be inherently less loud and accurate.
Back to airsoft - Was comapring with a friend with shorter silencer. He fitted mine which is about 2 inch longer and his shots are straight compared to his shorter silencer. Stock M4A1. My silencer has a spring core and sponge spacers inside. The sponge is cut about 1 inch and there are 5 of them evenly spaced out. Length of my silencer is 7 1/2 inches.