No you don't... Charizards hate being forced out because of this thing called *Stealth Rock* Go with Roar against all set up sweepers. Honestly, I don't think of this thing as having 4 move slot syndom at all. Roost + Moon Blast, Roar or Perish Song (you only need 1 usually), + 1 additional support move. Looks to be fine to me! Sure you can't do a lot of damage to Charizard Y, but just pack SR and watch Altaria's health.
You're right actually, although I can't help but nitpick and say that I did say later on that I personally didn't think it had 4MSS only that it might appear to, due to the many moves you may want to run. So, Roost, Moonblast, Roar/Perish Song, and Toxic would be my best bet for it, or Heal Bell. I can't think of anything else that it may want to run.