That is incorrect. Falstad Can hit the cannon with his Q while Grypctoers can also bomb it. Spawn 4 from Skybreaker and use Falstad Q and it's pretty much dead. You can try it now in game. Trust me bro, I rushed south as dwarves a million times... Tho it's true tho AoE also destroys the cannon easily. Antonidas fireball + Jainina Blizzard + Green's Balistas AoE ability and the cannon is gone in one sec.