Al I'm not understanding how you are coming to the conclusion that if I'm wings level and holding rudder that I have to be turning. The rudder is simply used to hold position relitive to the runway. This is the same tecnique that is used to keep box depth when flying IMAC or pattern. Imagine flying a constant line 150 ft beyond the runway but you have 10 knots of wind in your face. How would you keep the airplane from drifting in towards you?
If your wings are level and your rudder is not centered, then your plane is making a skidding turn in the direction in which you have the rudder deflected. This is not subject to argument. The plane will continue to yaw until the rudder is neutralized. You can fly a straight line in a crosswind by crabbing into the wind (though the nose of the plane will not be pointed in the direction it is flying). Or you can do it by slipping, but then the wings will not be level. You cannot do it by holding the rudder off center, because an off-center rudder induces yaw as long as it is off center. It doesn't somehow stop doing that just because the plane is where you want it to be. So unless you either return the rudder to neutral once you've achieved a good crab angle or counteract the yaw by dropping a wing, the yaw will continue: what would stop it? This isn't a matter of full-scale vs. models, it's basic stuff about what airplanes do.
As I said before, I think we mean different things by "holding rudder." I think you mean using the rudder to change the plane's heading so it stays where you want it to be; that's crabbing. Which is fine, but I still haven't heard a reason why (considerations of making things look nice for pattern judges aside) it's preferable to changing your heading in the usual way.