A VOICE FROM THE INFERNO: Well, you may be right, not having tried a fiddle. Certainly from the outside it sounds like the shrieking of demons....Anyway, you are right that the moment critique is the shift from the thumb to the fingers as you move south -- one reason for not just letting the thumb do all the work is that you can (later on) separate out the thumb to do double thumbing etc, and the fingers can be used in threes and twos and ones in different patterns. Or so I am told.....
yours, Peter T.