I agree about moving on from the 4th line. However, you think Johnston is an acceptable replacement for Martin? Martin is not good. However, Johnston simply isn't an NHL player. This is where the Isles shoot themselves in the foot: the 4th line can still be effective, but not over the course of 82 games. Maybe 50. If they had appropriate depth, they can spell guys like Martin and Clutterbuck over the course of the year to keep them "fresh" for the playoffs where their clutch, grab, and overall griminess is most valuable. But when you keep an AHL 4th liner on the team, you cannot do that as your already terrible 4th line is now unplayable against NHL talent.
I like when my teams don't waste roster spots. This organization is incredible at it.