We might have a 3rd line if Boyle were playing up to his abilities. Him, Pyatt and Miller have the makings right now of being a decent third line. But Boyle has been missing. Rangers have had a hard time integrating a lot of their forwards this year and Brian's game has regressed. Add on that Kreider has not found his game and a lot of the depth we were counting on has not come through.
On the question of MZA--he is not a 3rd liner either. He's too small and doesn't have the grit or enough defensive ability to fit into that kind of a role. He's more of a specialist type player and guys like Boyle, Halpern, Asham, Pyatt, Miller, Haley aren't good fits with him as linemates either. To be effective at all he has to play with other skilled players.