I doubt bunting plays 4th line... or has he been that bad
It's more the role than skill. Spezza and Simmonds aren't bad players. The forth line is a gritty, tough, difficult line to play. They need to be a problem for the other team and if they score all the better. You want all lines to score. The fourth line has to do other things, the more they can score while doing those things the better.