Agree 100%.
My father's 1:1 tug Meeching was twin screw, twin rudder. Screws turned outwards. As a youngster I spent days and days on board in the holidays and Dad, the other skippers and the mate taught me how to handle her, how to tow and much more. (It was assumed that I'd follow in the family tradition and probably end up as a tug skipper!) You could turn her on the spot with ease as described above, but you probably didn't want to use full rudder. You got to a point where adding more rudder seemed to weaken the turning motion. How that relates to model sized craft I don't know, I'll leave that to those with degrees in hydrodynamics!
I have two twin screw model tugs with independent control of motors. The bigger one has outwards turning screws but they're in Korts and I'm sure that negates some of the prop walk. But she'll still turn on the spot with one motor half ahead, one half astern and half rudder in the direction of the turn. The smaller one is Meeching, scratch built (very well!) by a modeller going from photos only - so he had no information of what she was like underwater. The screws are inwards turning on her but she still manages to turn well. As the shafts and props are out for a clean and lube, I'll swap the props over to match the real thing and see if it makes a difference.