On the contrary. Unison playing, yes, but there is a strong tradition of 'variation' in Irish music, and I know at least one banjo player who is a recognised master of it. This is not the same thing as free improvisation, but it does involve adapting melodies on the hoof, employing very few of the notes that you'd commit to paper if you were writing down the tune, but while maintaining the spirit of the melody. Done properly, the tune is still completely recognisable, and will fit with anyone else who is playing the 'unison' line - or other variations. It's what makes Irish music so intoxicatingly dangerous and uplifting when it's done properly. This skill is considered to be a high art in Irish tune playing. Scottish music, by contrast, must be played strictly as written. There is just room for the occasional snap or other ornamentation (not the same thing at all as variation), but if you vary the A pert of a Scottish tune you are in danger of finding you have already played the B or C part.