But not "should" of course, even though a performance of such a part of a tune over three repeats that doesn't include the slow roll at least once would seem perverse."
   michael, some of the traditional fiddle styles of Donegal,hardly use and sometimes very very rarely use the roll at all, but prefer the bowed ornament, that is not perverse, but fact. there is no obligation on anyone to use rolls, it is a matter of choice, the same applies to bowed ornamentation, bowed ornaments as are heard in Donegal were very rarely used in sliabh luchra, that is not perverses but just different style
playing the music right is subjective, in fact playing any music right is subjective.
to quote Carthy, the only harm you can do to a song is not sing it,
many airs are songs, some tunes were songs, lanigans ball, frost is all over,rocky road to dublin,follow me down to carlow, jolly beggarman, chase me charlie,shan van vocht etc., tunes and songs to a considerable extent are intertwined.